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                            NORTHWESTERN CORPORATION


                                       TO


                               JPMORGAN CHASE BANK


                                   as Trustee


                       -----------------------------------


                             SUPPLEMENTAL INDENTURE


                       Providing, among other things, for
          New Mortgage Bonds, Credit Agreement (2002) Series, due 2006


                       -----------------------------------


                          Dated as of February 1, 2003



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        SUPPLEMENTAL INDENTURE, dated as of February 1, 2003 (this "Supplemental
Indenture"),  made by and between  NORTHWESTERN  CORPORATION  (formerly known as
NorthWestern Public Service Company), a corporation organized and existing under
the laws of the State of Delaware (the  "Company"),  the post office  address of
which is 125 S. Dakota Avenue,  Suite 1100, Sioux Falls, South Dakota 57104, and
JPMORGAN CHASE BANK  (successor by merger to The Chase  Manhattan Bank (National
Association)),  a bank organized and existing under the laws of the State of New
York (the "Trustee"),  as Trustee under the General Mortgage  Indenture and Deed
of Trust  dated as of August 1, 1993,  hereinafter  mentioned,  the post  office
address of which is 4 New York Plaza, 15th Floor, New York, New York 10004;

        WHEREAS,  the Company has heretofore  executed and delivered its General
Mortgage  Indenture and Deed of Trust dated as of August 1, 1993 (the  "Original
Indenture"), to the Trustee, for the security of the Bonds of the Company issued
and to be issued thereunder (the "Bonds"); and

        WHEREAS,  the Company  has  heretofore  executed  and  delivered  to the
Trustee five indentures supplemental to the Original Indenture,  the first dated
as of August 15,  1993,  the  second  dated as of August 1, 1995 and each of the
third,  fourth and fifth dated as of September 1, 1995 (the Original  Indenture,
as supplemented and amended by the aforementioned  five supplemental  indentures
and  by  this  Supplemental  Indenture,  being  hereinafter  referred  to as the
"Indenture"); and

        WHEREAS,  the  Company  desires  to  create a new  series of Bonds to be
issued under the Indenture,  to be known as New Mortgage Bonds, Credit Agreement
(2002) Series,  due 2006 (the "New Mortgage Bonds of the Credit Agreement (2002)
Series"); and

        WHEREAS,  the  Company,  in the  exercise  of the powers  and  authority
conferred  upon and reserved to it under the  provisions of the  Indenture,  and
pursuant to appropriate resolutions of the Board of Directors, has duly resolved
and  determined  to make,  execute  and  deliver to the  Trustee a  Supplemental
Indenture in the form hereof for the purposes herein provided; and

        WHEREAS,  all  conditions  and  requirements   necessary  to  make  this
Supplemental  Indenture a valid,  binding and legal  instrument  have been done,
performed and  fulfilled and the execution and delivery  hereof have been in all
respects duly authorized;

        NOW, THEREFORE, THIS INDENTURE WITNESSETH:

        THAT NorthWestern Corporation, in consideration of the acceptance or the
purchase and  ownership (as  applicable)  from time to time of the Bonds and the
service by the Trustee and its successors, under the Indenture and of One Dollar
to it, duly paid by the Trustee at or before the ensealing and delivery of these
presents,  the receipt  whereof is hereby  acknowledged,  hereby  covenants  and
agrees  to and with the  Trustee  and its  successors  in the  trust  under  the
Indenture, for the benefit of those who shall hold the Bonds as follows:






                                    ARTICLE I
                 DESCRIPTION OF NEW MORTGAGE BONDS OF THE CREDIT
                            AGREEMENT (2002) SERIES

        SECTION 1. The Company  hereby creates a new series of Bonds to be known
as "New Mortgage  Bonds,  Credit  Agreement  (2002)  Series,  due 2006." The New
Mortgage  Bonds  of the  Credit  Agreement  (2002)  Series  shall  be  executed,
authenticated  and delivered in accordance  with the provisions of, and shall in
all respects be subject to, all of the terms,  conditions  and  covenants of the
Indenture,  as supplemented and modified.  The aggregate principal amount of New
Mortgage Bonds of the Credit  Agreement (2002) Series which may be authenticated
and delivered  under the Indenture  (except for New Mortgage Bonds of the Credit
Agreement  (2002)  Series  authenticated  and  delivered  upon  registration  of
transfer of, or in exchange for, or in lieu of, other New Mortgage  Bonds of the
Credit  Agreement  (2002)  Series  pursuant to the  Indenture and except for New
Mortgage  Bonds of the Credit  Agreement  (2002) Series  which,  pursuant to the
Indenture,  are deemed never to have been  authenticated and delivered under the
Indenture) is limited to $110,000,000.

        New Mortgage Bonds of the Credit Agreement (2002) Series shall be issued
to Credit Suisse First Boston,  acting  through its Cayman  Islands  Branch,  as
collateral agent (together with its successors in such capacity, the "Collateral
Agent") under the Bond Collateral  Agreement,  dated as of February 10, 2003 (as
amended or otherwise modified,  or as waived, or as replaced, in each case, from
time to time in accordance with its terms, the "Collateral Agreement"),  between
the Company and the Collateral  Agent,  to secure the obligations of the Company
to pay when due the Applicable  Share (as hereinafter  defined) of the principal
of and interest on the loans (the "Loans") made and outstanding under the Credit
Agreement,  dated as of December 17, 2002 (as amended or otherwise modified,  or
as waived,  or as replaced,  in each case,  from time to time in accordance with
its terms, the "Credit Agreement"),  among the Company, as borrower, the several
lenders from time to time  parties  thereto (the  "Lenders")  and Credit  Suisse
First Boston,  acting through its Cayman Islands Branch, as administrative agent
(together with its successors in such capacity, the "Administrative Agent").

        As used  herein,  "Applicable  Share"  means,  as of any day, a fraction
(expressed  as a  percentage  rounded  to the  eighth  decimal  place),  (i) the
numerator of which is the aggregate  principal  amount of the New Mortgage Bonds
of the Credit Agreement (2002) Series that are Outstanding on such day, and (ii)
the denominator of which is the sum of (a) the aggregate principal amount of the
New Mortgage Bonds of the Credit Agreement (2002) Series that are Outstanding on
such day, plus (b) the aggregate  principal  amount of the First Mortgage Bonds,
Credit  Agreement  (2002) Series,  due 2006, of the Company (the "Montana Credit
Agreement Bonds") that are outstanding on such day under the Company's  Mortgage
and Deed of Trust, dated as of October 1, 1945, relating (among other things) to
property acquired by the Company from NorthWestern Energy, L.L.C., which in turn
acquired   such  property  from  The  Montana  Power  Company  (as  amended  and
supplemented,  the "Montana Mortgage").  Initially, the Applicable Share will be
28.20512821%  (being  the  expression  as a  percentage  (rounded  to the eighth
decimal  place) of a  fraction,  the  numerator  of which is  $110,000,000  (the
aggregate  principal


                                       2



amount of the New Mortgage Bonds of the Credit  Agreement (2002) Series that are
to  be  issued  and  become   Outstanding)  and  the  denominator  of  which  is
$390,000,000 (the sum of $110,000,000, the aggregate principal amount of the New
Mortgage Bonds of the Credit  Agreement  (2002) Series that are to be issued and
become  Outstanding,  plus $280,000,000,  the aggregate  principal amount of the
Montana  Credit  Agreement  Bonds that are to be issued  and become  outstanding
under the Montana Mortgage  simultaneously with the issuance of the New Mortgage
Bonds  of the  Credit  Agreement  (2002)  Series).  Pursuant  to the  Collateral
Agreement,  the Collateral Agent will furnish to the Trustee (with a copy to the
Company) as soon as  practicable  after any change in the  Applicable  Share,  a
certificate,  signed by a person  purporting to be its duly authorized  officer,
notifying  the Trustee of such change in the  Applicable  Share (an  "Applicable
Share  Certificate").  Each Applicable Share Certificate shall set forth (i) the
changed  Applicable  Share,  (ii) the  date  such  change  occurred,  (iii)  the
aggregate  principal  amount of the New Mortgage  Bonds of the Credit  Agreement
(2002) Series then Outstanding,  and (iv) the aggregate  principal amount of the
Montana Credit Agreement Bonds then outstanding under the Montana Mortgage.  The
Trustee may  conclusively  presume  that the  Applicable  Share is  28.20512821%
unless and until the Trustee receives an Applicable Share Certificate. Following
receipt by the  Trustee of an  Applicable  Share  Certificate,  the  Trustee may
conclusively  presume  that  the  Applicable  Share  is as  set  forth  in  such
Applicable Share Certificate  unless and until the Trustee receives a subsequent
Applicable Share Certificate.

        New Mortgage Bonds of the Credit Agreement (2002) Series shall mature on
December 1, 2006 (the "Maturity Date"),  with an installment of principal of the
New Mortgage Bonds of the Credit  Agreement  (2002) Series in an amount equal to
$275,000  (said amount  representing  one quarter of one percent  (0.25%) of the
original  aggregate  principal  amount of the New  Mortgage  Bonds of the Credit
Agreement  (2002) Series) being payable on the last Business Day (as hereinafter
defined) of each March,  June,  September  and December  occurring  prior to the
Maturity  Date,  commencing  March 31, 2003, and the balance of the principal of
the New Mortgage  Bonds of the Credit  Agreement  (2002) Series being payable on
the Maturity Date; in each case,  unless an equal  installment or balance of the
principal  of the  Loans  is not due and  payable  on such  Business  Day or the
Maturity Date, as applicable,  in accordance with the Credit Agreement by reason
of prior prepayment of the Loans (in which event, there shall be due and payable
on the New Mortgage Bonds of the Credit Agreement (2002) Series on such Business
Day or on the Maturity Date, as applicable, an amount of principal of said bonds
equal to the  Applicable  Share of the amount of  principal of the Loans that is
payable  on  such  Business  Day or on the  Maturity  Date,  as  applicable,  in
accordance with the Credit  Agreement);  the unpaid  principal amount of the New
Mortgage Bonds of the Credit  Agreement (2002) Series shall bear interest at one
or more variable interest rates per annum which rate or rates for each day shall
be equal to the rate or rates per annum  borne by the Loans in  accordance  with
the Credit  Agreement  for such day  (calculated  in the manner  provided in the
Credit Agreement for the calculation of interest on the Loans),  payable on each
day on which  interest  is  payable on the Loans in  accordance  with the Credit
Agreement  (and in an  amount  equal to the  Applicable  Share of the  amount of
interest that is payable on the Loans on such day in accordance  with the Credit
Agreement) to the Collateral Agent, as the registered owner,  without regard to,
or


                                       3



necessity  for, any record date; the principal of and interest on each said Bond
to be  payable  at the  office  or  agency  of the  Company  in the  Borough  of
Manhattan,  The City of New York,  in such coin or currency of the United States
of  America as at the time of  payment  is legal  tender for public and  private
debts.  New Mortgage Bonds of the Credit  Agreement Series (2002) shall be dated
as in Section 3.03(c) of the Original Indenture (as supplemented)  provided.  As
used herein,  "Business Day" means a day other than a Saturday,  Sunday or other
day on which commercial banks in New York City are authorized or required by law
to close.

        As  permitted  pursuant to Sections  3.01 and 5.06 of the  Mortgage  (as
supplemented),  scheduled amortization payments with respect to the New Mortgage
Bonds of the Credit  Agreement  (2002) Series (as specified for the New Mortgage
Bonds of the Credit  Agreement (2002) Series prior to the Maturity Date pursuant
to the preceding paragraph of this Section 1) shall not constitute redemption in
part of the New  Mortgage  Bonds  of the  Credit  Agreement  (2002)  Series  for
purposes of Section  5.06 of the  Mortgage (as  supplemented)  (and,  therefore,
surrender of the New Mortgage Bonds of the Credit  Agreement (2002) Series shall
not be a condition to the receipt by the  registered  owners of the New Mortgage
Bonds of the  Credit  Agreement  (2002)  Series of such  scheduled  amortization
payments).

        SECTION 2. New  Mortgage  Bonds of the Credit  Agreement  (2002)  Series
shall be issued only as registered  Bonds without coupons of the denomination of
$1,000,  or any  integral  multiple  of $1 in  excess of  $1,000,  appropriately
numbered.  New  Mortgage  Bonds of the  Credit  Agreement  (2002)  Series may be
exchanged, upon surrender thereof, at the office or agency of the Company in the
Borough of Manhattan,  The City of New York,  State of New York, for one or more
New Mortgage  Bonds of the Credit  Agreement  (2002) Series of other  authorized
denominations, for the same aggregate principal amount, subject to the terms and
conditions set forth in the Indenture.

        New Mortgage  Bonds of the Credit  Agreement  (2002) Series shall not be
transferable  except to any  successor  Collateral  Agent  under the  Collateral
Agreement;  provided, however, that, subject to compliance with the registration
requirements of the Securities Act of 1933, as amended (the  "Securities  Act"),
(i) on or after the day on which the Loans are  accelerated  in accordance  with
the Credit  Agreement (the  "Acceleration  Day"), all (but not less than all) of
the  New  Mortgage  Bonds  of  the  Credit  Agreement  (2002)  Series  shall  be
transferable by the Collateral  Agent (together with all (but not less than all)
of the Montana  Credit  Agreement  Bonds) to or upon the order of the Lenders in
full  satisfaction and discharge of the Loans and the Obligations (as defined in
the Collateral  Agreement) pursuant to Section 4.1 of the Collateral  Agreement,
and (ii) following such transfer by the Collateral  Agent, New Mortgage Bonds of
the Credit  Agreement (2002) Series shall be transferable  (without  restriction
(except as  hereinafter  in the  following  two  paragraphs  described))  by the
registered owners thereof.

        As a condition  precedent to any  transfer of the New Mortgage  Bonds of
the Credit Agreement (2002) Series by the Collateral Agent, the Collateral Agent
shall submit to the Company,  the Trustee and the Bond Registrar (in addition to
all  other  documents  and  instruments  required  to be  submitted  to the Bond
Registrar  pursuant to the  Indenture) a


                                       4



certificate of the  Collateral  Agent,  signed by a person  purporting to be its
duly  authorized  officer,  certifying that the transferee in such transfer is a
successor   Collateral  Agent  under  the  Collateral   Agreement  or  that  the
transferees in such transfer are the Lenders or Persons specified by the Lenders
to which on or after the Acceleration Day all (but not less than all) of the New
Mortgage Bonds of the Credit  Agreement (2002) Series and all (but not less than
all) of the  Montana  Credit  Agreement  Bonds  are  being  transferred  in full
satisfaction  and discharge of the Loans and the  Obligations (as defined in the
Collateral  Agreement) pursuant to Section 4.1 of the Collateral  Agreement (and
the Trustee and the Bond  Registrar may  conclusively  presume the statements in
any such  certificate  of the  Collateral  Agent to be correct).  As a condition
precedent  to the  transfer  of any New  Mortgage  Bond of the Credit  Agreement
(2002)  Series to a  transferee  other than a successor  Collateral  Agent,  the
transferor  in such transfer  shall deliver to the Company,  the Trustee and the
Bond Registrar (in addition to all other documents and  instruments  required to
be submitted to the Bond Registrar  pursuant to the Indenture) (i) an opinion of
counsel  reasonably  satisfactory  to the  Company,  the  Trustee  and the  Bond
Registrar, or (ii) a certificate of the transferor in such transfer, signed by a
person purporting to be its duly authorized officer,  reasonably satisfactory to
the Company,  the Trustee and the Bond Registrar,  in either case, to the effect
that such transfer is either (A) covered by an effective  registration statement
of the Company under the Securities Act (setting forth the  registration  number
and the date of effectiveness  of such  registration  statement),  or (B) exempt
from  registration  under the  Securities  Act  (setting  forth  the  applicable
exemption from  registration  being relied upon and the reason such exemption is
applicable to such transfer).

        Any transfer of New Mortgage Bonds of the Credit Agreement (2002) Series
(i) shall be subject to the provisions of Section 3.05 of the Indenture,  except
that  the  provisions  of  paragraph  (g) of  such  Section  3.05  shall  not be
applicable to any transfer of New Mortgage Bonds of the Credit  Agreement (2002)
Series  which  occurs on or prior to the  Remedy  Exercise  Day (as  hereinafter
defined) (and the Company  hereby waives the  provisions of such  paragraph with
respect to any such transfer), and (ii) shall be made at the office or agency of
the Company in the Borough of Manhattan, The City of New York.

        The Company  hereby waives any right to make any charge for any exchange
or transfer of New Mortgage Bonds of the Credit  Agreement  (2002) Series by the
Collateral  Agent or any Person that is a direct  transferee  of the  Collateral
Agent  (but not by any other  transferee  of New  Mortgage  Bonds of the  Credit
Agreement  (2002) Series),  whether to reimburse  itself for any tax or taxes or
other  governmental  charge or otherwise (it being  understood  that the Company
shall pay any tax or taxes or  governmental or other charge which may be payable
by reason of any  exchange  or  transfer  of New  Mortgage  Bonds of the  Credit
Agreement  (2002) Series by the Collateral  Agent or any Person that is a direct
transferee of the Collateral Agent).  However, the Company reserves the right to
require payment of a sum sufficient to cover any tax or taxes or governmental or
other charge that may be imposed in connection  with any transfer or exchange of
New Mortgage Bonds of the Credit Agreement (2002) Series by any registered owner
other than the Collateral Agent or any Person that is a direct transferee


                                       5



of the Collateral Agent,  other than any exchange pursuant to Section 3.04, 5.06
or 14.06 of the Indenture not involving any transfer.

        The Company has  appointed  JPMorgan  Chase Bank as its agent to receive
New  Mortgage  Bonds  of  the  Credit   Agreement  (2002)  Series  presented  or
surrendered for payment,  to receive New Mortgage Bonds of the Credit  Agreement
(2002)  Series  surrendered  for  registration  of transfer  or exchange  and to
receive  notices  and  demands  to or upon the  Company  in  respect  of the New
Mortgage Bonds of the Credit Agreement (2002) Series and the Indenture;  and the
corporate  trust office of JPMorgan Chase Bank in the Borough of Manhattan,  The
City of New York, State of New York shall be the office or agency of the Company
in the Borough of  Manhattan,  The City of New York,  State of New York at which
such presentations, surrenders, notices and demands may be made or served.

        SECTION 3. The New Mortgage Bonds of the Credit  Agreement (2002) Series
and the Trustee's  Certificate of  Authentication  shall be substantially in the
following forms respectively:

        [The form of the New Mortgage Bond of the Credit Agreement (2002) Series
begins on the following page of this Supplemental Indenture.]


                                       6



         [FORM OF BOND OF THE CREDIT AGREEMENT (2002) SERIES, DUE 2006]

      TRANSFER OF THIS BOND IS SUBJECT TO CERTAIN RESTRICTIONS ON TRANSFER
       CONTAINED IN THE INDENTURE TO WHICH REFERENCE IS MADE IN THIS BOND.
      THE TRANSFER RESTRICTIONS ARE DESCRIBED ON THE REVERSE OF THIS BOND.

                            NORTHWESTERN CORPORATION
             (Incorporated under the laws of the State of Delaware)
           NEW MORTGAGE BOND, CREDIT AGREEMENT (2002) SERIES, DUE 2006

No. R-                                                            $_____________

        NorthWestern Corporation, a corporation organized and existing under the
laws of the State of  Delaware  (the  "Company",  which term shall  include  any
successor  corporation as defined in the Indenture hereinafter referred to), for
value  received,  hereby  promises to pay to Credit Suisse First Boston,  acting
through its Cayman Islands Branch, as collateral agent under the Bond Collateral
Agreement to which  reference is  hereinafter  made, or (subject to the transfer
restrictions  described on the reverse hereof)  registered  assigns,  the sum of
_________  dollars,  in installments prior to, and the balance on, the first day
of December,  2006 (the  "Maturity  Date"),  in each case,  in such amount as is
described  on the  reverse  hereof  for such  installment  or such  balance,  as
applicable, and in any coin or currency of the United States of America which at
the time of payment is legal  tender for public and  private  debts,  and to pay
interest thereon as described on the reverse hereof in like coin or currency.

        The Bonds of the  series of which  this Bond is one have been  issued to
Credit  Suisse  First  Boston,  acting  through its Cayman  Islands  Branch,  as
collateral agent (together with its successors in such capacity, the "Collateral
Agent") under the Bond Collateral  Agreement,  dated as of the date set forth on
the  reverse  hereof (as  amended or  otherwise  modified,  or as waived,  or as
replaced,  in each case,  from time to time in  accordance  with its terms,  the
"Collateral Agreement"), between the Company and the Collateral Agent, to secure
the  obligations  of the  Company  to pay  when  due the  Applicable  Share  (as
hereinafter defined) of the principal of and interest on the loans (the "Loans")
made and outstanding under the Credit  Agreement,  dated as of December 17, 2002
(as amended or otherwise modified,  or as waived, or as replaced,  in each case,
from time to time in accordance with its terms, the "Credit  Agreement"),  among
the Company, as borrower,  the several lenders from time to time parties thereto
(the  "Lenders")  and Credit  Suisse  First  Boston,  acting  through its Cayman
Islands Branch,  as  administrative  agent (together with its successors in such
capacity, the "Administrative Agent").

        This Bond shall not be entitled to any benefit  under the  Indenture  or
any  indenture  supplemental  thereto,  or become  valid or  obligatory  for any
purpose, until the form of certificate endorsed herein shall have been signed by
or on behalf of JPMorgan  Chase  Bank,  the Trustee  under the  Indenture,  or a
successor  trustee thereto under the Indenture,  or by an  authenticating  agent
duly appointed by the Trustee in accordance with the terms of the Indenture.

        The provisions of this Bond are continued on the reverse hereof and such
continued provisions shall for all purposes have the same effect as though fully
set forth at this place.

        IN WITNESS WHEREOF,  NorthWestern Corporation has caused this Bond to be
signed  (manually  or by  facsimile  signature)  in its  name  by an  Authorized
Executive  Officer,  as defined in the  Indenture,  and its corporate seal (or a
facsimile  thereof) to be hereto affixed and attested  (manually or by facsimile
signature) by an Authorized Executive Officer, as defined in the Indenture.

Dated:                               NORTHWESTERN CORPORATION
                                     By____________________________________
                                             Authorized Executive Officer
ATTEST:
By____________________________________
      Authorized Executive Officer




                [FORM OF TRUSTEE'S CERTIFICATE OF AUTHENTICATION]

        This is one of the Bonds of the series designated therein referred to in
the within-mentioned  Indenture and Supplemental  Indenture dated as of February
1, 2003.

                                     JPMORGAN CHASE BANK, AS TRUSTEE
                                     By____________________________________
                                               Authorized Officer



                                       7




                            [FORM OF REVERSE OF BOND]

Indenture and Series Designation
- --------------------------------

        This Bond is one of a duly authorized issue of bonds of the Company (the
"Bonds"), of the series hereinafter specified, all issued and to be issued under
and  equally  secured  by a General  Mortgage  Indenture  and Deed of Trust (the
"Indenture"),  dated as of August 1, 1993,  executed by the  Company  (under its
then name,  NorthWestern  Public  Service  Company) to The Chase  Manhattan Bank
(National Association),  the predecessor to JPMorgan Chase Bank (the "Trustee"),
as Trustee, to which Indenture and all indentures supplemental thereto reference
is hereby made for a description  of the properties  mortgaged and pledged,  the
nature and extent of the security,  the rights of registered owners of the Bonds
and of the Trustee in respect  thereof,  and the terms and conditions upon which
the Bonds are, and are to be, secured (and for the definition of any capitalized
term used herein but not defined herein (with any term defined herein and in the
Indenture  being  used  herein as defined  herein)).  The Bonds may be issued in
series,  for various  principal  sums, may mature at different  times,  may bear
interest at different rates and may otherwise vary as provided in the Indenture.
This  Bond is one of a series  designated  as the "New  Mortgage  Bonds,  Credit
Agreement  (2002)  Series,  due 2006"  (the "New  Mortgage  Bonds of the  Credit
Agreement  (2002)  Series")  of the  Company  issued  under and  secured  by the
Indenture and described in the  supplemental  indenture  dated as of February 1,
2003  (the  "Supplemental  Indenture")  between  the  Company  and the  Trustee,
supplemental to the Indenture.

Issuance to Collateral Agent under Collateral Agreement
- -------------------------------------------------------

        The Bonds of the Credit  Agreement (2002) Series have been issued to the
Collateral Agent under the Collateral Agreement to secure the obligations of the
Company to pay when due the  Applicable  Share (as  hereinafter  defined) of the
principal  of and  interest on the Loans made and  outstanding  under the Credit
Agreement. The Collateral Agreement is dated as of February 10, 2003.

Principal
- ---------

        Principal  of the New  Mortgage  Bonds of the  Credit  Agreement  (2002)
Series,  of which this Bond is one, is scheduled  to be paid as follows:  (A) on
the last Business Day (as hereinafter  defined) of each March,  June,  September
and December  occurring prior to the Maturity Date (commencing  March 31, 2003),
an installment  of principal of the New Mortgage  Bonds of the Credit  Agreement
(2002)  Series in an amount  equal to $275,000  (said  amount  representing  one
quarter of one percent (0.25%) of the original aggregate principal amount of the
New Mortgage  Bonds of the Credit  Agreement  (2002) Series) is due and payable;
and (B) on December 1, 2006 (the "Maturity Date"),  the balance of the principal
of the New  Mortgage  Bonds of the  Credit  Agreement  (2002)  Series is due and
payable;  in each case,  unless an equal installment or balance of the principal
of the Loans is not due and payable on such  Business Day or the Maturity  Date,
as  applicable,  in  accordance  with the  Credit  Agreement  by reason of prior
prepayment  of the Loans (in which event,  there shall be due and payable on the
New Mortgage Bonds of the Credit Agreement (2002) Series on such Business Day or
on the Maturity Date, as applicable,  an


                                       8



amount of principal of said Bonds equal to the Applicable Share of the amount of
principal  of the Loans that is payable on such  Business Day or on the Maturity
Date, as applicable,  in accordance with the Credit Agreement).  As used herein,
"Business  Day" means a day other than a Saturday,  Sunday or other day on which
commercial banks in New York City are authorized or required by law to close.

Interest
- --------

        The  unpaid  principal  amount of the New  Mortgage  Bonds of the Credit
Agreement  (2002)  Series,  of which this Bond is one,  bears interest at one or
more variable interest rates per annum which rate or rates for each day shall be
equal to the rate or rates per annum borne by the Loans in  accordance  with the
Credit  Agreement for such day  (calculated in the manner provided in the Credit
Agreement for the calculation of interest on the Loans),  payable on each day on
which interest is payable on the Loans in accordance  with the Credit  Agreement
(and in an amount equal to the  Applicable  Share of the amount of interest that
is payable on the Loans on such day in accordance with the Credit  Agreement) to
the Collateral Agent, as the registered  owner,  without regard to, or necessity
for, any record date.

Applicable Share
- ----------------

        As used  herein,  "Applicable  Share"  means,  as of any day, a fraction
(expressed  as a  percentage  rounded  to the  eighth  decimal  place),  (i) the
numerator of which is the aggregate  principal  amount of the New Mortgage Bonds
of the Credit Agreement (2002) Series that are Outstanding on such day, and (ii)
the denominator of which is the sum of (a) the aggregate principal amount of the
New Mortgage Bonds of the Credit Agreement (2002) Series that are Outstanding on
such day, plus (b) the aggregate  principal  amount of the First Mortgage Bonds,
Credit  Agreement  (2002) Series,  due 2006, of the Company (the "Montana Credit
Agreement  Bonds") that are outstanding on such day under the Company's  Montana
Mortgage (as defined in the Supplemental Indenture).

Redemption
- ----------

        New Mortgage Bonds of the Credit Agreement (2002) Series,  of which this
Bond is one, are subject to redemption as follows (but shall not otherwise be or
become  subject to redemption,  whether at the option of the holders  thereof or
the  Company  or  pursuant  to  any  other  requirements  or  provisions  of the
Indenture):  (A) on each day on which the Loans are  subject  to  prepayment  in
accordance with the Credit Agreement, New Mortgage Bonds of the Credit Agreement
(2002) Series shall be subject to redemption  in an aggregate  principal  amount
equal to the  Applicable  Share of the aggregate  principal  amount of the Loans
that are so subject to  prepayment  on such day; and (B) on the day on which the
Loans are accelerated in accordance with the Credit Agreement (the "Acceleration
Day"),  the entire  aggregate  principal amount of the New Mortgage Bonds of the
Credit Agreement (2002) Series shall be subject to redemption (the "Acceleration
Redemption");  in each case,  without  any  necessity  for notice or call by the
Trustee (such notice and call being waived by the  registered  owners of the New
Mortgage  Bonds of the Credit  Agreement  (2002) Series by the acceptance of the
New Mortgage Bonds of the Credit  Agreement (2002) Series and in connection with
each  Redemption  Demand (as


                                       9



hereinafter defined)).  Redemption of New Mortgage Bonds of the Credit Agreement
(2002) Series,  of which this Bond is one, shall be at a redemption  price equal
to the  principal  amount of such New  Mortgage  Bonds of the  Credit  Agreement
(2002)  Series  (without  premium),  together  with  interest  accrued  on  said
principal to and including the date of redemption  (collectively,  a "Redemption
Amount").  In the  event  of any  failure  by the  Company  to pay  when due the
Redemption  Amount with respect to any  redemption of New Mortgage  Bonds of the
Credit Agreement (2002) Series,  interest shall accrue on such unpaid Redemption
Amount at the rate or rates (and in amounts equal to the Applicable Share of the
amounts) of interest that accrue on the  corresponding  unpaid  principal of and
interest on the Loans in accordance with the Credit Agreement.

        The Trustee may conclusively  presume that no redemption of New Mortgage
Bonds of the Credit  Agreement  (2002)  Series is  required  unless and until it
shall have received a written notice from the Administrative  Agent, signed by a
person purporting to be its duly authorized officer,  stating that the Loans are
subject to  prepayment or have been  accelerated,  in either case, in accordance
with the Credit Agreement (a "Redemption  Demand").  Each Redemption Demand also
shall  state  the  date  on  which  the  Loans  are  subject  to  prepayment  or
acceleration in accordance with the Credit  Agreement,  the principal  amount of
the Loans subject to such prepayment or acceleration on such date, the principal
amount of the New Mortgage  Bonds of the Credit  Agreement  (2002)  Series to be
redeemed on such date in accordance with the Supplemental Indenture by reason of
such prepayment or acceleration,  and the Redemption Amount payable with respect
to such New Mortgage Bonds of the Credit Agreement (2002) Series  (determined in
accordance with the Supplemental  Indenture and setting forth the amounts of the
respective portions thereof  representing  principal of and interest on such New
Mortgage Bonds of the Credit  Agreement (2002) Series).  Each Redemption  Demand
shall be accompanied by a written waiver by the Collateral  Agent, as registered
owner of all of the New Mortgage  Bonds of the Credit  Agreement  (2002)  Series
then Outstanding, of notice of redemption and call for redemption by the Trustee
of the New  Mortgage  Bonds of the Credit  Agreement  (2002)  Series  subject to
redemption as described in such Redemption  Demand. The Trustee may conclusively
presume the statements contained in each Redemption Demand to be correct.

Additional Terms
- ----------------

        New  Mortgage  Bonds of the  Credit  Agreement  (2002)  Series  shall be
subject to the following other terms and conditions:

        (I) For the avoidance of any doubt (in the case of the following clauses
(i)  and  (ii))  and  notwithstanding  anything  herein  or in the  Supplemental
Indenture to the contrary other than the  provisions of subdivision  (III) below
(in the case of the following  clause (iii)):  (i) prior to the Remedy  Exercise
Day (as  hereinafter  defined),  each payment of principal of or interest on the
New Mortgage  Bonds of the Credit  Agreement  (2002) Series that becomes due and
payable  on any day  (whether  by  reason  of  stated  due  date,  acceleration,
redemption or otherwise)  shall  correspond  to, and be equal to the  Applicable
Share of, a payment of  principal  of or interest on the Loans that  becomes due
and payable on such day in  accordance  with the Credit  Agreement;  (ii) on the
Acceleration  Day,  the


                                       10



Redemption  Amount with respect to the Acceleration  Redemption shall be due and
payable;  and  (iii)  on and  after  the  Remedy  Exercise  Day (as  hereinafter
defined), (a) the Redemption Amount with respect to the Acceleration  Redemption
shall bear  interest (to the extent  permitted by law in the case of interest on
the portion of the  Redemption  Amount  representing  interest on the applicable
Bonds) at a  variable  rate per annum  which rate for each day shall be equal to
the Prime-Based Rate (as defined in the Supplemental Indenture and as calculated
by the Trustee) for such day plus 6.75%, payable to the registered owners of the
New Mortgage Bonds of the Credit  Agreement (2002) Series in the manner provided
in Section 3.07(b) of the Original  Indenture (as supplemented) or Section 10.07
of the Original  Indenture (as supplemented),  whichever is applicable,  and (b)
payments of principal  of and  interest on the New Mortgage  Bonds of the Credit
Agreement  (2002)  Series shall cease to  correspond to payments of principal of
and  interest on the Loans (and shall not be  satisfied  and  discharged  by the
satisfaction and discharge of the Loans).

        As used  herein,  "Remedy  Exercise  Day" means the day (on or after the
Acceleration Day) on which all (but not less than all) of the New Mortgage Bonds
of the  Credit  Agreement  (2002)  Series and all (but not less than all) of the
Montana Credit  Agreement  Bonds are  transferred by the Collateral  Agent to or
upon the order of the Lenders in full  satisfaction  and  discharge of the Loans
and the Obligations (as defined in the Collateral Agreement) pursuant to Section
4.1  of  the  Collateral  Agreement  (as  such  transfer  is  evidenced  by  the
registration  in the names of the  transferees in such transfer of  certificates
evidencing  all (but not less than all) of the New Mortgage  Bonds of the Credit
Agreement  (2002)  Series and all (but not less than all) of the Montana  Credit
Agreement Bonds). The Trustee may conclusively  presume that the Remedy Exercise
Day has not occurred  unless and until it shall have  received a written  notice
from  the  Collateral  Agent,  signed  by a  person  purporting  to be its  duly
authorized  officer,  stating that the Remedy  Exercise  Day has  occurred  (the
"Remedy  Exercise  Day  Notice").  The Remedy  Exercise Day Notice (i) shall set
forth the date of the Remedy Exercise Day, (ii) in the case of any such transfer
with  respect to which the  Trustee is not the  transfer  agent,  have  attached
thereto,  as evidence of the  transfer of the New  Mortgage  Bonds of the Credit
Agreement (2002) Series and the Montana Credit Agreement Bonds that gave rise to
the occurrence of the Remedy Exercise Day, copies of certificates  registered in
the names of the  transferees in such transfer of all (but not less than all) of
the New Mortgage  Bonds of the Credit  Agreement  (2002) Series and all (but not
less than all) of the Montana Credit  Agreement  Bonds,  and (iii) if the Remedy
Exercise  Day Notice is  received  by the Trustee on a day other than the Remedy
Exercise Day, the Prime Rate (as defined in the Supplemental Indenture) for each
day on and after the Remedy Exercise Day and on and prior to the Business Day on
which the Trustee  received  the Remedy  Exercise  Day  Notice.  The Trustee may
conclusively  presume the  statements  in the Remedy  Exercise  Day Notice to be
correct.

        (II) Prior to the Remedy  Exercise Day, the obligation of the Company to
make each payment of  principal of or interest on the New Mortgage  Bonds of the
Credit  Agreement  (2002) Series that becomes due and payable in accordance with
the  Supplemental  Indenture (i) shall be fully  satisfied and discharged if the
corresponding  payment of the  principal  of or interest on the Loans shall have
been fully  paid under and


                                       11



in accordance with the Credit Agreement,  and (ii) shall be partially  satisfied
and discharged if the  corresponding  payment of the principal of or interest on
the Loans shall have been partially paid under and in accordance with the Credit
Agreement  (such  partial  satisfaction  and  discharge  with respect to the New
Mortgage Bonds of the Credit Agreement (2002) Series to be in an amount equal to
the Applicable  Share of the amount of such partial  payment with respect to the
Loans). Without limitation of the foregoing, and for the avoidance of any doubt,
it is expressly stated that, prior to the Remedy Exercise Day, the Trustee shall
not be responsible for (i) the calculation of interest on the New Mortgage Bonds
of the Credit Agreement (2002) Series,  or (ii) the  determination of any amount
(including,  without limitation, any principal of or interest on the Loans) that
is payable or paid under the Credit Agreement.

        (III) Nothing in any of the New Mortgage  Bonds of the Credit  Agreement
(2002) Series  (including,  without  limitation,  any reference to the principal
payable with respect to the New Mortgage  Bonds of the Credit  Agreement  (2002)
Series being  determined on the basis of the  Applicable  Share of the principal
payable with respect to the Loans)  shall,  or shall be deemed or construed  to,
(i) increase the  aggregate  principal  amount of the New Mortgage  Bonds of the
Credit  Agreement  (2002) Series that are  Outstanding  from time to time,  (ii)
cause or permit an amount of principal  of the New Mortgage  Bonds of the Credit
Agreement (2002) Series to be or to become due and payable which,  when added to
all other principal of such Bonds theretofore  paid,  exceeds  $110,000,000,  or
(iii)  cause or permit  to be or  become  due and  payable  interest  on the New
Mortgage  Bonds of the Credit  Agreement  (2002)  Series which is payable on any
principal of the New Mortgage Bonds of the Credit  Agreement  (2002) Series that
is in excess of the principal of the New Mortgage Bonds of the Credit  Agreement
(2002) Series as restricted pursuant to the preceding clauses (i) and (ii).

Transfer Restrictions
- ---------------------

        New Mortgage  Bonds of the Credit  Agreement  (2002) Series shall not be
transferable  except to any  successor  Collateral  Agent  under the  Collateral
Agreement;  provided, however, that, subject to compliance with the registration
requirements of the Securities Act of 1933, as amended (the  "Securities  Act"),
(i) on or after  the  Acceleration  Day,  all (but not less than all) of the New
Mortgage Bonds of the Credit Agreement (2002) Series (together with all (but not
less than all) of the Montana Credit  Agreement  Bonds) shall be transferable by
the  Collateral  Agent to or upon the order of the Lenders in full  satisfaction
and  discharge of the Loans and the  Obligations  (as defined in the  Collateral
Agreement)  pursuant  to  Section  4.1 of the  Collateral  Agreement,  and  (ii)
following  such  transfer by the  Collateral  Agent,  New Mortgage  Bonds of the
Credit  Agreement  (2002)  Series  shall be  transferable  (without  restriction
(except as  hereinafter  in the  following  two  paragraphs  described))  by the
registered owners thereof.

        As a condition  precedent to any  transfer of the New Mortgage  Bonds of
the Credit Agreement (2002) Series by the Collateral Agent, the Collateral Agent
shall submit to the Company,  the Trustee and the Bond Registrar (in addition to
all  other  documents  and  instruments  required  to be  submitted  to the Bond
Registrar  pursuant to the  Indenture) a certificate  of the  Collateral  Agent,
signed by a person purporting to be its duly authorized


                                       12



officer,  certifying  that  the  transferee  in  such  transfer  is a  successor
Collateral Agent under the Collateral  Agreement or that the transferees in such
transfer  are the  Lenders or Persons  specified  by the  Lenders to which on or
after the Acceleration Day all (but not less than all) of the New Mortgage Bonds
of the  Credit  Agreement  (2002)  Series and all (but not less than all) of the
Montana Credit  Agreement Bonds are being  transferred in full  satisfaction and
discharge of the Loans pursuant to Section 4.1 of the Collateral  Agreement (and
the Trustee and the Bond  Registrar may  conclusively  presume the statements in
any such  certificate  of the  Collateral  Agent to be correct).  As a condition
precedent  to the  transfer  of any New  Mortgage  Bond of the Credit  Agreement
(2002)  Series to a  transferee  other than a successor  Collateral  Agent,  the
transferor shall deliver to the Company,  the Trustee and the Bond Registrar (in
addition to all other documents and instruments  required to be submitted to the
Bond Registrar  pursuant to the Indenture) (i) an opinion of counsel  reasonably
satisfactory  to the  Company,  the  Trustee and the Bond  Registrar,  or (ii) a
certificate of the transferor in such transfer, signed by a person purporting to
be its duly authorized  officer,  reasonably  satisfactory  to the Company,  the
Trustee and the Bond Registrar, in either case, to the effect that such transfer
is either (A)  covered by an  effective  registration  statement  of the Company
under the Securities Act (setting forth the registration  number and the date of
effectiveness of such registration  statement),  or (B) exempt from registration
under  the  Securities   Act  (setting  forth  the  applicable   exemption  from
registration  being relied upon and the reason such  exemption is  applicable to
such transfer).

        Any transfer of New Mortgage Bonds of the Credit Agreement (2002) Series
(i) shall be subject to the provisions of Section 3.05 of the Indenture,  except
that  the  provisions  of  paragraph  (g) of  such  Section  3.05  shall  not be
applicable to any transfer of New Mortgage Bonds of the Credit  Agreement (2002)
Series  which occurs on or prior to the Remedy  Exercise  Day, and (ii) shall be
made at the office or agency of the  Company in the  Borough of  Manhattan,  The
City of New York.

        The Company has waived any right to make any charge for any  exchange or
transfer of New  Mortgage  Bonds of the Credit  Agreement  (2002)  Series by the
Collateral  Agent or any Person that is a direct  transferee  of the  Collateral
Agent  (but not by any other  transferee  of New  Mortgage  Bonds of the  Credit
Agreement  (2002) Series),  whether to reimburse  itself for any tax or taxes or
other  governmental  charge or otherwise (it being  understood  that the Company
shall pay any tax or taxes or  governmental or other charge which may be payable
by reason of any  exchange  or  transfer  of New  Mortgage  Bonds of the  Credit
Agreement  (2002) Series by the Collateral  Agent or any Person that is a direct
transferee of the Collateral Agent).  However, the Company reserves the right to
require payment of a sum sufficient to cover any tax or taxes or governmental or
other charge that may be imposed in connection  with any transfer or exchange of
New Mortgage Bonds of the Credit Agreement (2002) Series by any registered owner
other than the Collateral Agent or any Person that is a direct transferee of the
Collateral  Agent,  other than any exchange  pursuant to Section  3.04,  5.06 or
14.06 of the Indenture not involving any transfer.



                                       13



General
- -------

        To  the  extent  permitted  by,  and  as  provided  in,  the  Indenture,
modifications or alterations of the Indenture,  or of any indenture supplemental
thereto,  and of the rights and obligations of the Company and of the holders of
the Bonds may be made with the consent of the Company by an affirmative  vote of
the holders of a majority in aggregate principal amount of the Bonds entitled to
vote then outstanding,  at a meeting of the holders of the Bonds called and held
as provided in the  Indenture,  and by an  affirmative  vote of the holders of a
majority in aggregate principal amount of the Bonds of any series or any tranche
or tranches of any series entitled to vote then outstanding and affected by such
modification or alteration,  in case one or more but less than all of the series
of Bonds or of any tranche or  tranches of any series of Bonds then  Outstanding
under  the  Indenture  are  so  affected;   provided,   however,  that  no  such
modification or alteration  shall be made which will affect the terms of payment
of the principal of, or interest or premium, if any, on this Bond.

        In case an Event of Default,  as defined in the Indenture,  shall occur,
the  principal  of all the New  Mortgage  Bonds of the Credit  Agreement  (2002)
Series at any such time  Outstanding  under the Indenture may be declared or may
become  due and  payable,  upon the  conditions  and in the  manner and with the
effect provided in the Indenture.  The Indenture  provides that such declaration
may be rescinded under certain circumstances.

                                   ARTICLE II
                       ISSUE OF NEW MORTGAGE BONDS OF THE
                         CREDIT AGREEMENT (2002) SERIES

        SECTION  1.  The  Company  hereby  exercises  the  right to  obtain  the
authentication of $62,500,000 principal amount of Bonds pursuant to the terms of
Section 4.03 of the Indenture. All such Bonds shall be New Mortgage Bonds of the
Credit Agreement (2002) Series.

        SECTION  2.  The  Company  hereby  exercises  the  right to  obtain  the
authentication of $47,500,000 principal amount of Bonds pursuant to the terms of
Section 4.04 of the Indenture. All such Bonds shall be New Mortgage Bonds of the
Credit Agreement (2002) Series.

        SECTION 3. Such New Mortgage Bonds of the Credit Agreement (2002) Series
may be  authenticated  and delivered prior to the filing for recordation of this
Supplemental Indenture.

                                  ARTICLE III
                         REDEMPTION AND OTHER PROVISIONS

        SECTION 1. New  Mortgage  Bonds of the Credit  Agreement  (2002)  Series
shall be subject to the following redemption and other terms and conditions:

        (I) New Mortgage  Bonds of the Credit  Agreement  (2002) Series shall be
subject to redemption  as follows (but shall not otherwise be or become  subject
to


                                       14



redemption,  whether at the  option of the  holders  thereof  or the  Company or
pursuant to any other requirements or provisions of the Indenture):  (A) on each
day on which the Loans are subject to prepayment  in accordance  with the Credit
Agreement,  New Mortgage  Bonds of the Credit  Agreement  (2002) Series shall be
subject to redemption in an aggregate  principal  amount equal to the Applicable
Share of the  aggregate  principal  amount of the Loans  that are so  subject to
prepayment on such day; and (B) on the  Acceleration  Day, the entire  aggregate
principal amount of the New Mortgage Bonds of the Credit Agreement (2002) Series
shall be subject to redemption (the  "Acceleration  Redemption");  in each case,
without any  necessity  for notice or call by the Trustee  (such notice and call
being waived by the  registered  owners of the New Mortgage  Bonds of the Credit
Agreement  (2002)  Series by the  acceptance  of the New  Mortgage  Bonds of the
Credit  Agreement  (2002) Series and in connection with each  Redemption  Demand
hereinafter described). Redemption of New Mortgage Bonds of the Credit Agreement
(2002) Series shall be at a redemption  price equal to the  principal  amount of
such New Mortgage Bonds of the Credit Agreement (2002) Series (without premium),
together  with interest  accrued on said  principal to and including the date of
redemption (collectively, a "Redemption Amount"). In the event of any failure by
the Company to pay when due the Redemption Amount with respect to any redemption
of New Mortgage  Bonds of the Credit  Agreement  (2002)  Series,  interest shall
accrue on such  unpaid  Redemption  Amount at the rate or rates  (and in amounts
equal to the  Applicable  Share of the  amounts) of interest  that accrue on the
corresponding  unpaid  principal of and interest on the Loans in accordance with
the Credit Agreement.

        The Trustee may conclusively  presume that no redemption of New Mortgage
Bonds of the  Credit  Agreement  (2002)  Series  is  required  pursuant  to this
subdivision  (I) unless and until it shall have  received a written  notice from
the  Administrative  Agent,  signed  by a  person  purporting  to  be  its  duly
authorized  officer,  stating that the Loans are subject to  prepayment  or have
been  accelerated,  in either case, in accordance  with the Credit  Agreement (a
"Redemption Demand").  Each Redemption Demand also shall state the date on which
the Loans are subject to  prepayment  or  acceleration  in  accordance  with the
Credit  Agreement,  the principal amount of the Loans subject to such prepayment
or acceleration on such date, the principal  amount of the New Mortgage Bonds of
the Credit  Agreement  (2002)  Series to be redeemed on such date in  accordance
with this  Supplemental  Indenture by reason of such prepayment or acceleration,
and the Redemption Amount payable with respect to such New Mortgage Bonds of the
Credit Agreement (2002) Series  (determined in accordance with this Supplemental
Indenture  and setting  forth the  amounts of the  respective  portions  thereof
representing  principal of and interest on such Bonds).  Each Redemption  Demand
shall be accompanied by a written waiver by the Collateral  Agent, as registered
owner of all of the New Mortgage  Bonds of the Credit  Agreement  (2002)  Series
then Outstanding, of notice of redemption and call for redemption by the Trustee
of the New  Mortgage  Bonds of the Credit  Agreement  (2002)  Series  subject to
redemption as described in such Redemption  Demand. The Trustee may conclusively
presume the statements contained in each Redemption Demand to be correct.

        (II)  For the  avoidance  of any  doubt  (in the  case of the  following
clauses (i) and (ii)) and  notwithstanding  anything herein or in any of the New
Mortgage Bonds of the


                                       15



Credit  Agreement  (2002)  Series to the contrary  other than the  provisions of
subdivision (IV) below (in the case of the following clause (iii)): (i) prior to
the Remedy Exercise Day (as hereinafter  defined),  each payment of principal of
or interest on the New Mortgage Bonds of the Credit Agreement (2002) Series that
becomes  due  and  payable  on any  day in  accordance  with  this  Supplemental
Indenture  (whether by reason of stated due date,  acceleration,  redemption  or
otherwise)  shall  correspond  to,  and be equal to the  Applicable  Share of, a
payment of principal of or interest on the Loans that becomes due and payable on
such day in accordance with the Credit Agreement;  (ii) on the Acceleration Day,
the Redemption  Amount with respect to the Acceleration  Redemption shall be due
and  payable;  and (iii) on and after the Remedy  Exercise  Day (as  hereinafter
defined), (a) the Redemption Amount with respect to the Acceleration  Redemption
shall bear  interest (to the extent  permitted by law in the case of interest on
the portion of the  Redemption  Amount  representing  interest on the applicable
Bonds) at a  variable  rate per annum  which rate for each day shall be equal to
the Prime-Based  Rate (as hereinafter  defined and as calculated by the Trustee)
for such day plus 6.75%,  payable to the  registered  owners of the New Mortgage
Bonds of the Credit  Agreement  (2002) Series in the manner  provided in Section
3.07(b) of the Original  Indenture  (as  supplemented)  or Section  10.07 of the
Original Indenture (as supplemented),  whichever is applicable, and (b) payments
of principal of and interest on the New Mortgage  Bonds of the Credit  Agreement
(2002) Series shall cease to correspond to payments of principal of and interest
on the Loans (and shall not be satisfied and discharged by the  satisfaction and
discharge of the Loans).

        As used  herein,  "Remedy  Exercise  Day" means the day (on or after the
Acceleration Day) on which all (but not less than all) of the New Mortgage Bonds
of the  Credit  Agreement  (2002)  Series and all (but not less than all) of the
Montana Credit  Agreement  Bonds are  transferred by the Collateral  Agent to or
upon the order of the Lenders in full  satisfaction  and  discharge of the Loans
and the Obligations (as defined in the Collateral Agreement) pursuant to Section
4.1  of  the  Collateral  Agreement  (as  such  transfer  is  evidenced  by  the
registration  in the names of the  transferees in such transfer of  certificates
evidencing  all (but not less than all) of the New Mortgage  Bonds of the Credit
Agreement  (2002)  Series and all (but not less than all) of the Montana  Credit
Agreement Bonds). The Trustee may conclusively  presume that the Remedy Exercise
Day has not occurred  unless and until it shall have  received a written  notice
from  the  Collateral  Agent,  signed  by a  person  purporting  to be its  duly
authorized  officer,  stating that the Remedy  Exercise  Day has  occurred  (the
"Remedy  Exercise  Day  Notice").  The Remedy  Exercise Day Notice (i) shall set
forth  (i) the date of the  Remedy  Exercise  Day,  (ii) in the case of any such
transfer  with  respect to which the  Trustee is not the  transfer  agent,  have
attached  thereto,  as evidence of the transfer of the New Mortgage Bonds of the
Credit  Agreement (2002) Series and the Montana Credit Agreement Bonds that gave
rise to the  occurrence  of the  Remedy  Exercise  Day,  copies of  certificates
registered in the names of the transferees in such transfer of all (but not less
than all) of the New Mortgage  Bonds of the Credit  Agreement  (2002) Series and
all (but not less than all) of the Montana Credit  Agreement Bonds, and (iii) if
the Remedy  Exercise  Day Notice is  received by the Trustee on a day other than
the Remedy Exercise Day, the Prime Rate (as hereinafter defined) for each day on
and after the Remedy  Exercise Day and on and prior to the Business Day on


                                       16



which the Trustee  received  the Remedy  Exercise  Day  Notice.  The Trustee may
conclusively  presume the  statements  in the Remedy  Exercise  Day Notice to be
correct.

        As used herein,  "Prime-Based  Rate" means, with respect to a particular
day (on or after the Remedy Exercise Day), the higher rate per annum of: (i) the
"Prime  Rate" (as  hereinafter  defined)  for such day;  and (ii) 4.0%.  As used
herein, "Prime Rate" means, with respect to a particular day, the "Prime-1 Rate"
for such day as such rate shall appear on the Business Day next  succeeding such
day on the display on Moneyline Telerate,  Inc. or any successor service on page
128 or any page that may replace page 128 on such service;  provided that (a) if
such day is not a Business  Day,  the Prime Rate for such day shall be such rate
for the next  preceding  Business  Day as so  appearing  on the next  succeeding
Business  Day,  and  (b) if no such  rate so  appears  on such  next  succeeding
Business Day, the Prime Rate for such day shall be the "prime rate" for such day
(or, if such day is not a Business Day, for the next preceding  Business Day) as
such rate appears on the next succeeding Business Day in the Wall Street Journal
under the  caption  "Money  Rates" (or if the Wall Street  Journal  ceases to be
published or of general  circulation,  such other financial journal or newspaper
of general circulation as is selected by the Trustee);  provided further that if
no rate so  appears  on such next  succeeding  Business  Day in the Wall  Street
Journal or such other financial journal or newspaper of general circulation, the
Prime  Rate for such day shall be the Prime Rate in effect  with  respect to the
day on which  the  Prime  Rate  was last  determinable  in  accordance  with the
foregoing  provisions of this  definition;  and provided  further that the Prime
Rate for each day on and after the Remedy  Exercise  Day and on and prior to the
Business Day on which the Trustee  received the Remedy Exercise Day Notice shall
be (i) the rate stated in the Remedy  Exercise  Day Notice as the Prime Rate for
such day, or (ii) if no such rate for such day is stated in the Remedy  Exercise
Day Notice, the Prime Rate for the Business Day next succeeding the Business Day
on which the Trustee  received the Remedy  Exercise Day Notice (as determined in
accordance with the foregoing provisions of this definition).

        (III) Prior to the Remedy Exercise Day, the obligation of the Company to
make each payment of  principal of or interest on the New Mortgage  Bonds of the
Credit  Agreement  (2002) Series that becomes due and payable in accordance with
this  Supplemental  Indenture (i) shall be fully satisfied and discharged if the
corresponding  payment of the  principal  of or interest on the Loans shall have
been fully  paid under and in  accordance  with the Credit  Agreement,  and (ii)
shall be partially satisfied and discharged if the corresponding  payment of the
principal of or interest on the Loans shall have been  partially  paid under and
in accordance with the Credit Agreement (such partial satisfaction and discharge
with respect to the New Mortgage Bonds of the Credit  Agreement (2002) Series to
be in an amount  equal to the  Applicable  Share of the  amount of such  partial
payment  with  respect to the  Loans).  Prior to the Remedy  Exercise  Day,  the
Trustee may  conclusively  presume  that the  obligation  of the Company to make
payments with respect to the principal of and interest on New Mortgage  Bonds of
the  Credit  Agreement  (2002)  Series  shall  have  been  fully  satisfied  and
discharged  unless and until the Trustee  shall have  received a written  notice
from the  Administrative  Agent,  signed by a person  purporting  to be its duly
authorized  officer,  stating  (i) that the  Company  has failed to make  timely
payment in full or in part of an amount of principal


                                       17



of and/or  interest on the Loans which became due and payable in accordance with
the Credit  Agreement,  (ii) the amount and date of such payment of principal of
and/or  interest on the Loans which the Company has failed to make in accordance
with the Credit Agreement,  and (iii) the amount of principal of and/or interest
on the New  Mortgage  Bonds of the Credit  Agreement  (2002)  Series  which,  in
accordance  with  this  Supplemental  Indenture,  has  not  been  satisfied  and
discharged  by  reason  of  such  failure  of  the  Company.   The  Trustee  may
conclusively  presume  the  statements  contained  in any such  notice  from the
Administrative Agent to be correct (unless and until the Trustee shall receive a
subsequent and/or modified notice from the Administrative  Agent pursuant to and
in accordance with this subdivision III).  Without  limitation of the foregoing,
and for the avoidance of any doubt,  it is expressly  stated that,  prior to the
Remedy  Exercise  Day,  the  Trustee  shall  not  be  responsible  for  (i)  the
calculation of interest on the New Mortgage Bonds of the Credit Agreement (2002)
Series, or (ii) the determination of any amount (including,  without limitation,
any  principal  of or  interest  on the Loans) that is payable or paid under the
Credit Agreement.

        (IV) Nothing  herein or in any of the New  Mortgage  Bonds of the Credit
Agreement (2002) Series  (including,  without  limitation,  any reference to the
principal payable with respect to the New Mortgage Bonds of the Credit Agreement
(2002)  Series  being  determined  on the basis of the  Applicable  Share of the
principal  payable  with  respect  to the  Loans)  shall,  or shall be deemed or
construed  to, (i) increase the aggregate  principal  amount of the New Mortgage
Bonds of the Credit  Agreement  (2002) Series that are Outstanding  from time to
time,  (ii) cause or permit an amount of principal of the New Mortgage  Bonds of
the Credit  Agreement  (2002)  Series to be or to become due and payable  which,
when  added to all other  principal  of such  Bonds  theretofore  paid,  exceeds
$110,000,000,  or (iii)  cause or  permit  to be or to  become  due and  payable
interest on the New Mortgage Bonds of the Credit  Agreement  (2002) Series which
is payable on any  principal of the New Mortgage  Bonds of the Credit  Agreement
(2002)  Series that is in excess of the  principal of the New Mortgage  Bonds of
the Credit  Agreement  (2002)  Series as  restricted  pursuant to the  preceding
clauses (i) and (ii).

        (V)  The  provisions  of  Sections  1.l6  and  3.07(b)  of the  Original
Indenture  shall not be  applicable  with respect to New  Mortgage  Bonds of the
Credit  Agreement Series (2002) prior to the Remedy Exercise Day (the provisions
of such Bonds  establishing  the dates for payment of principal  and interest on
such Bonds prior to the Remedy  Exercise Day being in lieu of the  provisions of
Section 1.16 of the Original Indenture).

                                   ARTICLE IV
                   ADDITIONAL COVENANT FOR THE BENEFIT OF THE
            NEW MORTGAGE BONDS OF THE CREDIT AGREEMENT (2002) SERIES

        SECTION 1. The Company covenants that so long as any of the New Mortgage
Bonds of the Credit  Agreement (2002) Series shall remain  Outstanding,  (i) the
Company  shall not submit a request to the  Trustee  or  otherwise  apply to the
Trustee for (a) the  authentication  and  delivery of Bonds  pursuant to Article
Four  of the  Original  Indenture  (as  supplemented),  (b) the  application  of
insurance  proceeds  pursuant  to Section  6.07 of the  Original  Indenture  (as
supplemented), (c) the release of property (including the


                                       18



withdrawal of proceeds of insurance or other cash)  pursuant to Article Eight of
the Original Indenture (as  supplemented),  or (d) the execution and delivery of
an indenture  supplemental  to the  Indenture  (any such request or  application
being  referred to as an  "Application"),  in any such case,  unless the Company
shall have given to the  Administrative  Agent,  at least the Required Number of
Days (as  hereinafter  defined)  prior to the  submission to the Trustee of such
Application,  notice of its  intention to apply to the Trustee for the taking of
such action (an "Administrative Agent Notice"),  and (ii) the Company shall have
furnished to the  Trustee,  in addition to the other  materials  required by the
provisions of the Original  Indenture (as  supplemented)  to be furnished to the
Trustee as part of such Application,  a copy of the Administrative  Agent Notice
with respect to such Application and an Officer's Certificate to the effect that
at least the Required Number of Days has elapsed subsequent to the giving by the
Company to the  Administrative  Agent of the  Administrative  Agent  Notice with
respect to such  Application  and prior to the submission to the Trustee of such
Application  (an  "Administrative  Agent  Notice  Certificate").  Receipt by the
Trustee of a copy of the  Administrative  Agent  Notice  and the  Administrative
Agent Notice  Certificate with respect to an Application  shall be conditions to
any action applied for in such Application.  As used herein, "Required Number of
Days" means, with respect to an Application, three (3) Business Days (as defined
in Article I, Section 1 of this  Supplemental  Indenture) or such shorter period
of time to which the Administrative  Agent shall have agreed in writing. For the
avoidance of doubt,  it is  expressly  stated that (i) an  Administrative  Agent
Notice may cover one or more different Applications and/or one or more different
actions to be taken pursuant to the same or different provisions of the Original
Indenture (as supplemented), and (ii) notwithstanding the number of Applications
or actions covered by an Administrative  Agent Notice, such Administrative Agent
Notice  need be given by the Company to the  Administrative  Agent only once (at
least the Required  Number of Days prior to the submission to the Trustee of the
first Application covered by such Administrative Agent Notice).

                                   ARTICLE V
                             AMENDMENTS TO MORTGAGE

        SECTION 1. Section  1.03 of the Original  Indenture is amended by adding
at the end thereof the following additional paragraph:

               Notwithstanding anything herein to the contrary, (i) with respect
        to the Net Earnings  Certificate required as a condition to the issuance
        of New Mortgage Bonds of the Credit  Agreement (2002) Series pursuant to
        Section 4.03 and, if applicable, Section 4.04 of the Original Indenture,
        and (ii) with respect to each Net Earnings  Certificate  required at any
        time at which (a) any of the New Mortgage Bonds of the Credit  Agreement
        (2002) Series are Outstanding under the Indenture, and (b) any bonds are
        outstanding  under the Montana  Mortgage,  the "Adjusted Net Earnings of
        the  Company"  shall  be,  and  shall be  stated  in such  Net  Earnings
        Certificate  to be,  the lesser of (A) the  amount  (for the  applicable
        period  selected in accordance  with paragraph (a) of this Section 1.03)
        determined  in accordance  with  paragraph (a) of this Section 1.03 (and
        the other  provisions  of this  Section  1.03 that are  relevant to such
        paragraph)  on the basis of (i) the items


                                       19



        set forth in clauses (i) and (ii) of paragraph  (a) of this Section 1.03
        being such portions of such items of the Company as have been reasonably
        allocated by the Company to or from the Mortgaged Property as a plant or
        plants  and  an  operating  system  or  operating  systems  in a  manner
        consistent with the manner of allocation  utilized and/or to be utilized
        by the Company in making  calculations  of the "Adjusted Net Earnings of
        the Company" under and as defined in the Montana Mortgage,  and (ii) the
        item set forth in clause  (iv) of  paragraph  (a) of this  Section  1.03
        being  calculated  without  regard to income derived by the Company from
        any  electric  and/or gas  utility  business of the Company in which the
        Mortgaged  Property is not utilized (but  otherwise in  accordance  this
        Section 1.03), and (B) the amount (for the applicable period selected in
        accordance  with  paragraph  (a) of this  Section  1.03)  determined  in
        accordance  with  paragraph  (a) of this  Section  1.03  (and the  other
        provisions  of this Section  1.03 that are  relevant to such  paragraph)
        (without any allocation or distinction as to the derivation of the items
        set forth in any of the clauses of paragraph  (a) of this Section  1.03,
        other than allocation or distinction between (i) the electric and/or gas
        utility  business or businesses in which the Company is engaged (whether
        or not the Mortgaged Property is utilized in connection therewith),  and
        (ii) the other  business or businesses  (if any) in which the Company is
        engaged (with such other business or businesses being given effect under
        the item set  forth in  clause  (iv) of  paragraph  (a) of this  Section
        1.03).  Each such Net Earnings  Certificate shall contain a statement of
        the signers of such Net  Earnings  Certificate  that,  in the opinion of
        such signers,  the allocations made in the calculations of "Adjusted Net
        Earnings of the Company" as set forth in such Net  Earnings  Certificate
        are in accordance with the  requirements of this final paragraph of this
        Section 1.03.

                                   ARTICLE VI
                                   THE TRUSTEE

        The Trustee hereby accepts the trust hereby  declared and provided,  and
agrees to perform the same upon the terms and  conditions  in the  Indenture set
forth and upon the following terms and conditions:

        The Trustee shall not be responsible in any manner  whatsoever for or in
        respect of the validity or sufficiency of this Supplemental Indenture or
        the due  execution  hereof by the  Company  or for or in  respect of the
        recitals contained herein, all of which recitals are made by the Company
        solely.  In  general,  each and every term and  condition  contained  in
        Article  Eleven  of the  Indenture  shall  apply  to  this  Supplemental
        Indenture  with the same force and effect as if the same were herein set
        forth in full, with such omissions, variations and modifications thereof
        as may be  appropriate  to make the same  conform  to this  Supplemental
        Indenture.



                                       20



                                  ARTICLE VII
                            MISCELLANEOUS PROVISIONS

        Except as otherwise  defined herein,  all capitalized terms used in this
Supplemental  Indenture have the meanings stated in the Original  Indenture,  as
heretofore supplemented.

        This Supplemental Indenture may be simultaneously executed in any number
of  counterparts,  each of  which  when so  executed  shall be  deemed  to be an
original;  but such counterparts shall together  constitute but one and the same
instrument.

                            [Signature Pages Follow]


                                       21




        IN  WITNESS   WHEREOF,   NorthWestern   Corporation   has  caused   this
Supplemental  Indenture to be executed on its behalf by an Authorized  Executive
Officer as defined in the Indenture, and its corporate seal to be hereto affixed
and said seal and this  Supplemental  Indenture to be attested by an  Authorized
Executive  Officer as defined in the  Indenture;  and  JPMorgan  Chase Bank,  in
evidence  of its  acceptance  of the  trust  hereby  created,  has  caused  this
Supplemental  Indenture to be executed on its behalf by its  President or one of
its Vice  Presidents  and its corporate  seal to be hereto affixed and said seal
and this  Supplemental  Indenture to be attested by its  Secretary or one of its
Vice Presidents; all as of the 1st day of February, 2003.

                                NORTHWESTERN CORPORATION


                                By   /s/ Eric R. Jacobsen
                                    ------------------------------------
                                    Eric R. Jacobsen

(CORPORATE SEAL)

ATTEST:


 /s/ Alan D. Dietrich
- ------------------------------------
         Alan D. Dietrich



                                JPMORGAN CHASE BANK


                                By   /s/ L. O'Brien
                                    --------------------------------------------
                                    Vice President

(CORPORATE SEAL)

ATTEST:



/s/ William G. Keenan
- ------------------------------------
         Vice President







STATE OF SOUTH DAKOTA               )
                                    ) SS
COUNTY OF MINNEHAHA                 )

        BE IT REMEMBERED,  that on this 10th day of February,  2003,  before me,
Karen L. Smook,  a Notary Public within and for the County and State  aforesaid,
personally came Eric R. Jacobsen, Senior Vice President,  General Counsel, Chief
Legal Officer and  Assistant  Corporate  Secretary  and an Authorized  Executive
Officer (as such term is defined in the  Indenture  referred to in the foregoing
Supplemental  Indenture)  and Alan D. Dietrich,  the Corporate  Secretary and an
Authorized  Executive Officer (as such term is defined in the Indenture referred
to in the foregoing  Supplemental  Indenture)  of  NorthWestern  Corporation,  a
Delaware  corporation,  who are personally known to me to be such officers,  and
who are  personally  known to me to be the same  persons  who  executed  as such
officers the within  instrument of writing,  and such persons duly  acknowledged
that they signed,  sealed and  delivered  the said  instrument as their free and
voluntary act as such officers and as the free and voluntary act of NorthWestern
Corporation for the uses and purposes therein set forth.

        IN WITNESS  WHEREOF,  I have hereunto  subscribed my name and affixed my
official seal on the day and year last above written.

                                            /s/ Karen L. Smook
                                            ------------------------------------
                                                      Karen L. Smook
                                           Notary Public, Minnehaha County, S.D.
{NOTARIAL SEAL)                               My Commission expires 7-12-2005






STATE OF NEW YORK                   )
                                    ) SS
COUNTY OF NEW YORK                  )

        BE IT REMEMBERED,  that on this 10th day of February,  2003,  before me,
Emily  Fayan,  a Notary  Public  within and for the County and State  aforesaid,
personally  came L. O'Brien,  a Vice  President,  and William G. Keenan,  a Vice
President,  of JPMorgan Chase Bank, a bank organized under the laws of the State
of New York,  who are personally  known to me to be such  officers,  and who are
personally  known to me to be the same persons who executed as such officers the
within  instrument  of writing,  and such  persons duly  acknowledged  that they
signed,  sealed and  delivered  the said  instrument as their free and voluntary
act,  each as such Vice  President and as the free and voluntary act of JPMorgan
Chase Bank for the uses and purposes therein set forth.

        IN WITNESS  WHEREOF,  I have hereunto  subscribed my name and affixed my
official seal on the day and year last above written.

                                           /s/ Emily Fayan
                                           Emily Fayan
                                           Notary Public, State of New York
                                           No. 01FA4737006
                                           Qualified in Kings County
                                           Certificate Filed in New York County
(NOTARIAL SEAL)                            Commission expires Dec. 31, 2005