SUPPLEMENTAL INDENTURE, dated as of __________, 1995 (the "Supplemental
Indenture"), made by and between 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 33 Third Street, S.E., Huron,
South Dakota 57350, and THE CHASE MANHATTAN BANK (National Association), a
national banking association organized and existing under the laws of the United
States of America (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 Chase MetroTech Center, 3rd Floor,
Brooklyn, New York 11245;

         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
Trustees a certain indenture supplemental to the Original Indenture dated August
15, 1993 (the Original Indenture, as supplemented and amended by the
aforementioned supplemental indenture 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, ___% Series due
2___ (the "New Mortgage Bonds of the ___% Series"), and to modify the Original
Indenture in certain respects; 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 Public Service Company, in consideration of the
purchase and ownership 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 BONDS OF THE ___% SERIES DUE 2___

         Section 1. The Company hereby creates a new series of Bonds to be known
as "New Mortgage Bonds, ___% Series due 2___." The New Mortgage Bonds of the
___% 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 commencement of the first interest period for the New Mortgage
Bonds of the ___% Series shall be __________, 1995. The New Mortgage Bonds of
the ___% Series shall mature __________, 2___, and shall bear interest at the
rate of (___%) per annum, payable semi-annually on the _____ day of __________
and the _____ day of __________ in each year. The person in whose name any of
the New Mortgage Bonds of the ___% Series are registered at the close of
business on any record date (as hereinafter defined) with respect to any
interest payment date shall be entitled to receive the interest payable on such
interest payment date notwithstanding the cancellation of such New Mortgage
Bonds of the ___% Series upon any transfer or exchange subsequent to the record
date and prior to such interest payment date; PROVIDED, HOWEVER, that if and to
the extent the Company shall default in the payment of the interest due on such
interest payment date, such defaulted interest shall be paid as provided in
Section 3.07(b) of the Indenture.

         The term "record date" as used in this Section with respect to any
interest payment date shall mean the __________ or __________, as the case may
be, next preceding the semi-annual interest payment date, or, if such __________
or _________ shall be a legal holiday or a day on which banking institutions in
the Borough of Manhattan, The City of New York, State of New York, are
authorized by law to close, then the next preceding day which shall not be a
legal holiday or a day on which such institutions are so authorized to close.

         Section 2. The New Mortgage Bonds of the ___% Series shall be issued
only as registered Bonds without coupons of the denomination of $1,000, or any
integral multiple of $1,000, appropriately numbered. The New Mortgage Bonds of
the ___% Series may be exchanged, upon surrender thereof, at the agency of the
Company in the Borough of Manhattan, The City of New York, State of New York,
for one or more new New Mortgage Bonds of the ___% 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 ___% Series may be exchanged or transferred
without expense to the registered owner thereof except that any taxes or other
governmental charges required to be paid with respect to such transfer or
exchange shall be paid by the registered owner requesting such transfer or
exchange as a condition precedent to the exercise of such privilege.

         Section 3. The New Mortgage Bonds of the ___% Series and the Trustee's
Certificate of Authentication shall be substantially in the following forms
respectively:

                   [FORM OF BOND OF THE ___% SERIES DUE 2___]

                       NORTHWESTERN PUBLIC SERVICE COMPANY
           (Incorporated under the laws of the State of South Dakota)
                     NEW MORTGAGE BOND, ___% SERIES DUE 2___

No. R-                                                           $______________

         Northwestern Public Service Company, 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 __________ or
registered assigns, the sum of __________ dollars on the _____ day of
__________, 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 in like coin or currency from

                                       -2-





__________, 1995, payable semi-annually, on the _____ days of __________ and
__________ in each year, at the rate of (___%) per annum, until the Company's
obligation with respect to the payment of such principal shall be discharged as
provided in the Indenture hereinafter mentioned. The interest so payable on any
__________ or __________ will, subject to certain exceptions provided in the
Supplemental Indenture dated as of __________, 1995, be paid to the person in
whose name this Bond is registered at the close of business on the immediately
preceding __________ or __________, as the case may be. Both principal of, and
interest on, this Bond are payable at the agency of the Company in the Borough
of Manhattan, The City of New York, State of New York.

         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 hereon shall have been signed by
or on behalf of The Chase Manhattan Bank (National Association), 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 New Mortgage 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 Public Service Company has caused this
New Mortgage Bond to be signed (manually or by facsimile signature) in its name
by an Authorized Executive Officer, as defined in this 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 this Indenture.

Dated:                                       NORTHWESTERN PUBLIC SERVICE COMPANY


                                             By
                                               ---------------------------------
                                                  AUTHORIZED EXECUTIVE OFFICER
ATTEST:


- ---------------------------------------------
         AUTHORIZED EXECUTIVE OFFICER

                         [FORM OF TRUSTEE'S CERTIFICATE]

         This is one of the Bonds of the series designated therein referred to
in the within-mentioned Indenture and Supplemental Indenture dated as of
_________, 1995.

                                             THE CHASE MANHATTAN BANK (NATIONAL
                                             ASSOCIATION), AS TRUSTEE


                                             By
                                               ---------------------------------
                                                      AUTHORIZED OFFICER


                                       -3-





                            [FORM OF REVERSE OF BOND]

         This New Mortgage Bond of the ___% Series 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 to The Chase Manhattan Bank (National Association)
(the "Trustee"), as Trustee, to which Indenture and all indentures supplemental
thereto reference is hereby made for a description to 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. 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 New Mortgage Bond of the ___% Series is one of a series
designated as the "New Mortgage Bonds, ___% Series Due 2___" (the "New Mortgage
Bonds of the ___% Series") of the Company issued under and secured by the
Indenture and described in the supplemental indenture dated as of __________,
1995 (the "Supplemental Indenture dated as of __________, 1995"), between the
Company and the Trustee, supplemental to the Indenture.

                     [Insert Redemption Terms-if applicable]

         To the extent permitted by, and as provided in, the Indenture,
modifications or alterations of the Indenture, or of any indenture supplemental
thereof, 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 ___% 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 ___% SERIES

         Section 1. The Company hereby exercises the right to obtain the
authentication of $__________ principal amount of Bonds pursuant to the terms of
Section _____ of the Indenture.
All such Bonds shall be New Mortgage Bonds of the ___% Series.

         Section 2. Such New Mortgage Bonds of the ___% Series may be
authenticated and delivered prior to the filing for recordation of this
Supplemental Indenture.


                                       -4-





                                   ARTICLE III
                                   REDEMPTION

         [Insert Redemption Terms-if applicable] [New Mortgage Bonds of the ___%
Series shall not be redeemable at any time prior to maturity.]

                                   ARTICLE IV
                         AMENDMENT OF ORIGINAL INDENTURE

         Section 4.02(b)(i) of the Original Indenture is hereby amended by
deleting it in its entirety and by inserting in lieu thereof the following:

                  (i) Class "A" Bonds (A) maturing on such dates and in such
         principal amounts that, at each Stated Maturity of the Bonds of such
         series (or the Tranche thereof then to be authenticated and delivered)
         that are to be authenticated and delivered pursuant to this Section
         4.02 (which may be less than the entire amount of the series or Tranche
         then to be issued), there shall mature Class "A" Bonds equal in
         principal amount to the principal amount of the Bonds of such series or
         Tranche so authenticated and delivered then to mature, and (B)
         containing, in addition to any mandatory redemption provisions
         applicable to all Class "A" Bonds Outstanding under the related Class
         "A" Mortgage, mandatory redemption provisions correlative to the
         provisions, if any, for the mandatory redemption (pursuant to a sinking
         fund or otherwise) of the Bonds of such series or Tranche so
         authenticated and delivered or for the redemption thereof at the option
         of the Holder; it being expressly understood that such Class "A" Bonds
         (1) may, but need not, bear interest, any such interest to be payable
         at the same times as interest on the Bonds of such series or Tranche so
         authenticated and delivered, (2) may, but need not, contain provisions
         for the redemption thereof at the option of the Company, any such
         redemption to be made at a redemption price or prices not less than the
         principal amount thereof, and (3) shall be held by the Trustee in
         accordance with Article Seven;

                                    ARTICLE V
                                   THE TRUSTEE

         The Trustee hereby accepts the trusts hereby declared 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.


                                       -5-





                                   ARTICLE VI
                            MISCELLANEOUS PROVISIONS

         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.

         IN WITNESS WHEREOF, said Northwestern Public Service Company has caused
this 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 Indenture to be attested by an Authorized Executive Officer
as defined in the Indenture; and The Chase Manhattan Bank (National
Association), in evidence of its acceptance of the trust hereby created, has
caused this 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 Indenture to be attested by its Secretary or one of its Assistant
Secretaries; all as of the _____ day of __________, 1995.

                                             NORTHWESTERN PUBLIC SERVICE COMPANY


                                             By
                                               ---------------------------------
                                                        VICE PRESIDENT

(CORPORATE SEAL)

ATTEST:


- --------------------------------
     [ASSISTANT] SECRETARY
                                             THE CHASE MANHATTAN BANK (NATIONAL
                                             ASSOCIATION)


                                             By
                                               ---------------------------------
                                                        VICE PRESIDENT

(CORPORATE SEAL)

ATTEST:


- --------------------------------
       ASSISTANT SECRETARY

                                       -6-





STATE OF SOUTH DAKOTA  )
                       )  SS
COUNTY OF BEADLE       )

         BE IT REMEMBERED, that on this _____th day of __________, 1995, before
me, ___________, a Notary Public within and for the County and State aforesaid,
personally came _________, Vice President, and __________, [Assistant] Corporate
Secretary of Northwestern Public Service Company, 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 Vice
President and [Assistant] Corporate Secretary, respectively, and as the free and
voluntary act of Northwestern Public Service Company 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.

(NOTARIAL SEAL)
                                              ----------------------------------
                                                       Notary Public
                                                         [NAME]
                                            Notary Public, Beadle County, S.D.
                                         My Commission expires __________, _____







STATE OF NEW YORK      )
                       )  SS
COUNTY OF KINGS        )


         BE IT REMEMBERED, that on this _____th day of __________, 1995, before
me, ___________, a Notary Public within and for the County and State aforesaid,
personally came _________, Vice President, and __________, Assistant Secretary
of The Chase Manhattan Bank (National Association), a national banking
association, 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 Vice President and Assistant Secretary, respectively, and as the free
and voluntary act of The Chase Manhattan Bank (National Association) 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.



(NOTARIAL SEAL)
                                              ----------------------------------
                                                       Notary Public

                                              Notary Public, State of New York
                                              No.__________
                                              Qualified in Kings County
                                              Commission expires _________, ____