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THIRD MODIFICATION TO AMENDED AND RESTATED BUSINESS LOAN AND SECURITY AGREEMENT

          THIS THIRD MODIFICATION TO AMENDED AND RESTATED BUSINESS LOAN AND
SECURITY AGREEMENT (this "Modification") is made as of the 9th day of November,
1998, by and among (i) NATIONSBANK, N.A., a national banking association
("NationsBank"), having an office at 8300 Greensboro Drive, Suite 550, McLean,
Virginia 22102; (ii) FLEET CAPITAL CORPORATION, a Rhode Island corporation
("Fleet"), having an office at 300 Galleria Parkway Northwest, Suite 800,
Atlanta, Georgia 30339; (iii) each other person or entity hereafter becoming a
"Lender" pursuant to the hereinafter defined Loan Agreement; (iv) NATIONSBANK,
N.A., a national banking association (acting in its capacity as Agent for the
Lenders), having an office at 8300 Greensboro Drive, Suite 550, McLean, Virginia
22102; (v) BTG, INC., a Virginia corporation; BTG TECHNOLOGY SYSTEMS, INC., a
Virginia corporation formerly known as BDS, Inc.; DELTA RESEARCH CORPORATION, a
Virginia corporation; CONCEPT AUTOMATION, INC. OF AMERICA, a Virginia
corporation; and NATIONS, INC., a New Jersey corporation (collectively, the
"Borrowers"); all having principal offices at 3877 Fairfax Ridge Road, 4B,
Fairfax, Virginia 22030-7448; and (vi) each other person or entity hereafter
executing a "Joinder Agreement" pursuant to the Loan Agreement. Capitalized
terms used but not defined herein shall have the meanings attributed to such
terms in the Loan Agreement.

                        W I T N E S S E T H  T H A T:

          WHEREAS, pursuant to the terms and conditions of that certain Amended
and Restated Business Loan and Security Agreement dated October 31, 1997 (as
heretofore amended and as the same may be hereafter amended or modified, the
"Loan Agreement"), by and among the Agent, Borrowers, Lenders and Crestar Bank
(acting in its capacity as a Lender), the Borrowers obtained a loan (the "Loan")
from the Lenders in the original aggregate maximum principal amount of One
Hundred Ten Million and No/100 Dollars ($110,000,000.00), which aggregate
maximum principal amount had been heretofore reduced to Sixty Million Dollars
($60,000,000), but continues to be evidenced by two (2) separate Replacement
Revolving Promissory Notes (as defined in Exhibit A), in the aggregate original
maximum principal amount of Ninety-five Million Dollars ($95,000,000), and which
Loan is secured by, among other things, certain collateral more fully described
in Article III, Section 1 of the Loan Agreement; and

          WHEREAS, the Borrowers have requested an extension of the maturity
date of the Loan, a modification of the Borrowing Base and a modification of
certain financial covenants set forth in the Loan Agreement; and

          WHEREAS, the Agent and Lenders have agreed to extend the maturity date
of the Loan, modify the Borrowing Base and modify certain financial covenants
set forth in the Loan Agreement, subject to the terms of this Modification,
provided that the Loan Agreement is further modified to reduce the Commitment
Amount and increase the
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Additional Libor Percentage applicable to amounts outstanding from time to time
on a LIBOR basis, as hereinafter provided.

          NOW, THEREFORE, for Ten Dollars ($10.00) and other good and valuable
consideration, the receipt and sufficiency of which are hereby acknowledged, the
parties hereto agree as follows:


          1.    The foregoing recitals are hereby incorporated herein by this
reference and made a part hereof, with the same force and effect as if fully set
forth herein.


          2.    The maturity date of the Loan shall be August 31, 2002, unless
sooner accelerated pursuant to the terms of the Loan Agreement, the Note or any
other Loan Document. Simultaneously with the Borrowers' execution and delivery
of this Modification, the Borrowers shall execute and deliver to the Agent, for
and on behalf of the Lenders (as applicable), an Allonge and First Modification
to Replacement Revolving Promissory Note No. 1 and an Allonge and First
Modification to Replacement Revolving Promissory Note No. 2, in form and
substance reasonably acceptable to the Lenders, evidencing the extension of the
maturity date.


          3.    The definitions of "Commitment Amount" and "Consolidated Fixed
Charges" set forth in the "Certain Definitions" section of the Loan Agreement
are hereby deleted in their entirety and the following substituted in lieu
thereof:


                ""COMMITMENT AMOUNT" shall mean Fifty Million and No/100
                Dollars ($50,000,000.00).


                "CONSOLIDATED FIXED CHARGES" shall mean, as of the date of the
                particular determination, interest expenses, plus current
                maturities of long term debt, plus current maturities of
                capitalized leases, plus cash payments for taxes for the fiscal
                quarter of the Borrowers most recently ended (excluding,
                however, taxes paid on profits from the sale of Cisco Systems,
                Inc. stock), calculated on a consolidated basis in accordance
                with GAAP."


          4.    The following definitions of "Eligible Billed Foreign Accounts
Receivable" and "Maturity Date" are hereby added to the "Certain Definitions"
section of the Loan Agreement:

                ""ELIGIBLE BILLED FOREIGN ACCOUNTS RECEIVABLE" shall mean
                Receivables which (i) represent amounts due and owing for
                products actually delivered and accepted or work or services

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                actually performed or rendered by or on behalf of any Borrower
                pursuant to any contract or agreement now or hereafter entered
                into by the particular Borrower and any unrelated and
                unaffiliated non-domestic entity; (ii) have been properly
                billed; (iii) arise in the ordinary course of the particular
                Borrower's business; (iv) are due, owing and not subject to any
                defense, set-off or counterclaim; and (v) are specifically
                approved in writing in advance by the Agent.

                "MATURITY DATE" shall mean the maturity date set forth in the
                Notes."


          5.    Section 3(a) of Article I of the Loan Agreement is hereby
deleted in its entirety and the following substituted in lieu thereof:


                "(a) Maximum Advances. Notwithstanding any term or provision of
                this Agreement or any other Loan Document to the contrary, it
                is understood and agreed that in no event whatsoever shall the
                Lenders be obligated to advance any amount or have Obligations
                outstanding pursuant hereto which shall exceed the lesser of:

                        1.   The Commitment Amount, or

                        2.   The aggregate of (the "Maximum Borrowing Base"):

                             (i) ninety percent (90%) of the Borrowers' Eligible
                             Borrowing Base Receivables representing amounts due
                             and owing from the Government, which are
                             outstanding less than one hundred twenty-one (121)
                             days from the date of original invoice; plus

                             (ii) eighty-five percent (85%) of the Borrowers'
                             Eligible Borrowing Base Receivables representing
                             amounts due and owing from domestic account debtors
                             (other than the Government), which are outstanding
                             less than ninety-one (91) days from the date of
                             original invoice; plus

                             (iii) the lesser of (y) fifty percent (50%) of the
                             Borrower's Eligible Unbilled Costs; or (z) Ten
                             Million Dollars ($10,000,000); plus

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                             (iv) the lesser of (y) eighty percent (80%) of the
                             Borrower's Eligible Billed Foreign Accounts
                             Receivable; or (z) Three Million Dollars
                             ($3,000,000.00).

                        All receivables included in the computation of the
                        Maximum Borrowing Base must be acceptable to the Agent
                        in all respects. Each request for an advance shall be
                        deemed a representation by the Borrowers that any
                        Eligible Borrowing Base Receivable, Eligible Unbilled
                        Cost and Eligible Billed Foreign Accounts Receivable on
                        which such request is based satisfies the foregoing
                        requirements."


          6.    The last sentence of Section 8 of Article I of the Loan
Agreement is hereby deleted in its entirety and the following substituted in
lieu thereof:


                        "Notwithstanding the foregoing, the Termination Fee
                        shall not be payable in connection with a permanent
                        reduction of the Commitment Amount, if such permanent
                        reduction is made (A) after the date which is
                        twenty-four (24) months after the date hereof, or (B) in
                        connection with (y) a contemporaneous bond offering,
                        provided that such bond offering (1) is consummated
                        prior to March 31, 1998, and (2) does not exceed One
                        Hundred Million Dollars ($100,000,000), in the
                        aggregate, or (z) a contemporaneous public stock
                        offering or public or private sale of BTG, any
                        Subsidiary or any of their respective collective assets
                        (with no new replacement indebtedness or debt
                        refinancing of any kind, directly or indirectly)."


          7.    The last sentence of Section 1 of Article II of the Loan
Agreement is hereby deleted in its entirety and the following substituted in
lieu thereof:


                        "No Letter of Credit shall be issued which, by its
                        terms, expires after the Maturity Date."


          8.    Section 15(a) of Article VI of the Loan Agreement is hereby
deleted in its entirety and the following substituted in lieu thereof:


                        "(a) Tangible Net Worth. The Borrowers, on a
                        consolidated basis, will maintain at all times during
                        the following periods, Tangible Net Worth of not less
                        than the following amounts:


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                                    Periods                          Required Tangible Net Worth
                                                                      
                        From September 30, 1998 through                  $21,500,000.00
                        December 30, 1998
                        
                        From December 31, 1998 through March             $23,750,000.00
                        30, 1999
                        
                        From March 31, 1999 through the                  $23,750,000.00, plus 67% of
                        Maturity Date                                    net income (as determined on
                                                                         a consolidated basis in
                                                                         accordance with GAAP at the
                                                                         end of each fiscal quarter)


                        For purposes of this Agreement, "Tangible Net Worth"
                        shall mean all capital stock, paid in capital and
                        retained earnings, less all treasury stock, amounts due
                        from officers, directors, stockholders and members of
                        their immediate families, amounts due from affiliates
                        (to the extent such amounts are part of the Borrowers'
                        consolidated net worth), investments in non-marketable
                        securities, notes receivable of affiliates (to the
                        extent that such amounts are part of the Borrowers'
                        consolidated net worth), leasehold improvements,
                        goodwill, non-competition agreements, capitalized
                        organization and development costs, capitalized
                        expenses, loan costs, patents, trademarks, copyrights,
                        franchises, licenses and other intangible assets."


          9. Section 6 of Exhibit 7 to the Loan Agreement is hereby deleted in
its entirety and the following substituted in lieu thereof:


                        "The term Additional Libor Percentage shall mean the
                        percentage which corresponds to the Borrowers' "Leverage
                        Ratio", as set forth below:

                                                                 Additional
                        Leverage Ratio                        Libor Percentage

                        greater than or equal to 7.0 to 1.0          3.25%


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                        greater than or equal to 6.0 to 1.0,
                        but less than 7.0 to 1.0                     3.00%

                        greater than or equal to 5.0 to 1.0,
                        but less than 6.0 to 1.0                     2.75%

                        greater than or equal to 4.0 to 1.0,
                        but less than 5.0 to 1.0                     2.50%

                        less than 4.0 to 1.0                         2.25%


                        For purposes hereof the Borrowers' "Leverage Ratio"
                        shall mean the ratio of Borrowers' Funded Debt to
                        Consolidated EBITDA, as calculated in accordance with
                        Section 15(c) of Article VI of the Loan Agreement.
                        Determinations of the applicable Additional Libor
                        Percentage shall be made quarterly, on or before the
                        first (1st) day of each February, May, August and
                        November throughout the term of the Loan (the 1st day of
                        each such month being herein referred to as a
                        "Calculation Date"), based on the quarterly financial
                        statements submitted by the Borrowers for the
                        immediately preceding calendar quarter; it being
                        understood and agreed that if any such quarterly
                        financial statements are not submitted as required
                        hereunder, the applicable Additional Libor Percentage
                        for the ensuing Quarterly Period shall be three and
                        one-quarter percent (3.25%). The applicable Additional
                        Libor Percentage so determined shall be effective for
                        any Interest Period which commences on or after the
                        applicable Calculation Date, and such rate shall
                        continue to be the applicable Additional Libor
                        Percentage until the next Calculation Date (each such
                        period of effectiveness being herein referred to as a
                        "Quarterly Period"). Each Borrower expressly
                        acknowledges and agrees that nothing set forth in this
                        Section 6 of Exhibit 7 to the Loan Agreement shall
                        alter, amend or modify in any respect the Borrowers'
                        obligations to comply with each and all of the financial
                        covenants set forth in Section 15 of Article VI of the
                        Loan Agreement."


          10.   Simultaneously with the effectiveness of this Modification,
Exhibit 5 to the Loan Agreement shall be deleted in its entirety and Exhibit 5
attached to this Modification shall be substituted in lieu thereof.


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          11.   Notwithstanding anything contained in the Loan Agreement to the
contrary, the Libor Interest Election option shall not be available until and
unless Borrowers receive written notification from the Agent.


          12.   Each Borrower hereby acknowledges, agrees, represents and
warrants that, as of the date hereof (i) there are no set-offs or defenses
against the Notes, the Loan Agreement or any other Loan Document; (ii) except
as specifically amended hereby, all of the terms and conditions of the Notes,
the Loan Agreement and the other Loan Documents shall remain unmodified and in
full force and effect; (iii) the Notes, the Loan Agreement (as modified hereby)
and the other Loan Documents are hereby expressly approved, ratified and
confirmed; and (v) the execution, delivery and performance by each Borrower of
this Modification (a) is within its corporate powers, (b) has been duly
authorized by all necessary corporate action, and (c) does not require the
consent or approval of any other person or entity.


          13.   The Borrowers shall pay all of the Agent's costs and expenses
associated with this Modification and the transactions referenced herein or
contemplated hereby, including, without limitation, the Agent's reasonable
legal fees and expenses.


          14.   This Modification shall be governed by the laws of the
Commonwealth of Virginia and shall be binding upon and inure to the benefit of
the parties hereto and their respective successors and assigns.


          15.   This Modification may be executed in any number of
counterparts, each of which shall be deemed an original and all of which
together shall be deemed one and the same instrument.


      [remainder of page intentionally left blank - signature page follows]

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          IN WITNESS WHEREOF, the undersigned have signed, sealed and delivered
this Modification on the day and year first above written.


                                                   

                                                       BORROWERS:
                                                       ----------

[Corporate Seal]                                       BTG, INC.,
ATTEST:                                                a Virginia corporation



By:/s/ MARILYNN D. BERSOFF                             By:        /s/ EDWARD H. BERSOFF
   ----------------------------------                             ------------------------------
Name:          Marilynn D. Bersoff                     Name:      Edward H. Bersoff
Title:         Secretary                               Title:     President and CEO


[Corporate Seal]                                       BTG TECHNOLOGY SYSTEMS, INC., 
ATTEST:                                                a Virginia corporation



By:/s/ MARILYNN D. BERSOFF                             By:        /s/ EDWARD H. BERSOFF
   ----------------------------------                             ------------------------------

Name:          Marilynn D. Bersoff                     Name:      Edward H. Bersoff
Title:         Secretary                               Title:     President


[Corporate Seal]                                       DELTA RESEARCH CORPORATION,
ATTEST:                                                a Virginia corporation


By:/s/ MARILYNN D. BERSOFF                             By:        /s/ EDWARD H. BERSOFF
   ----------------------------------                             ------------------------------

Name:          Marilynn D. Bersoff                     Name:      Edward H. Bersoff
Title:         Secretary                               Title:     CEO


[Corporate Seal]                                       CONCEPT AUTOMATION, INC. OF
ATTEST:                                                AMERICA, a Virginia corporation


By:/s/ MARILYNN D. BERSOFF                             By:        /s/ EDWARD H. BERSOFF
   ----------------------------------                             ------------------------------

Name:          Marilynn D. Bersoff                     Name:      Edward H. Bersoff
Title:         Secretary                               Title:     CEO



                  [signatures continue on the following page]

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Corporate Seal]                                        NATIONS, INC.,
ATTEST:                                                a New Jersey corporation


By:/s/ MARILYNN D. BERSOFF                             By:        /s/ EDWARD H. BERSOFF
   ----------------------------------                             ------------------------------

Name:          Marilynn D. Bersoff                     Name:      Edward H. Bersoff
Title:         Secretary                               Title:     President and CEO


                                                       AGENT:

                                                       NATIONSBANK, N.A., a
                                                       national banking association, acting in its
                                                       capacity as Agent


                                                       By:        /s/ DOUGLAS T. BROWN
                                                                  ------------------------------
                                                       Name:      Douglas T. Brown
                                                       Title:     Vice President


                                                       LENDER(S):

                                                       NATIONSBANK, N.A., a
                                                       national banking association


                                                       By:        /s/ DOUGLAS T. BROWN
                                                                  ------------------------------
                                                       Name:      Douglas T. Brown
                                                       Title:     Vice President

                                                       FLEET CAPITAL CORPORATION, a
                                                       Rhode Island corporation


                                                       By:        /s/ STUART J. SOLOMON
                                                                  ------------------------------
                                                       Name:      Stuart J. Solomon
                                                       Title:     Senior Vice President





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                                    EXHIBIT A

For purposes of this Modification, "Replacement Revolving Promissory Notes"
shall have the meaning attributed to the term "Notes" in the Loan Agreement.