Document:

<PAGE>

                                                                  EXHIBIT 10.2.1

June 16, 2000

Mr. William J. Lindenmayer
President
International Fuel Technology, Inc.
7777 Bonhomme, Suite 1920
St. Louis, MO 63105

                                Re:  GEM Global Yield Fund Limited ("GEM")
                                     Debenture Purchase Agreement
                                     -------------------------------------

Dear Mr. Lindenmayer:

We represent GEM with regard to the Debenture Purchase Agreement between
International Fuel Technology, Inc. ("IFUE") and GEM, dated February 25, 2000
(the "Agreement").

As per the terms of the Agreement, IFUE is to have taken effective with the
Securities and Exchange Commission (the "SEC") a registration statement with
regard to the Underlying Shares, as defined in the Agreement, no later than
June 24, 2000 (the "Deadline"). IFUE is liable to GEM for certain penalties in
the event the Deadline is not met.

As per your request, GEM is willing to extend the Deadline to August 24, 2000,
under the following conditions:

     1.  The Warrants, as defined in the Agreement, are delivered to GEM no
         later than June 24, 2000.

     2.  The first sentence of Section 4.(c)(i) of the Agreement is modified to
         read:

         "(c) (i)  The Conversion Price for each Debenture in effect on any
         Conversion Date shall be the lesser of (X) $0.8125 or 125% of the
         average closing bid price for the five (5) Trading Days immediately
         prior to the Closing Date ("Fixed Conversion Price") or (Y) 91%
         (ninety-one percent) of the average of the three (3) lowest closing bid
         prices during the twenty (20) day period ("Three Day Average Closing
         Bid Price") immediately preceding the Conversion Date ("Floating
         Conversion Price")."

     3.  The Purchase Price, as defined in the Agreement, is modified to read
         "$1,500,000.00."

<PAGE>

International Fuel Technology, Inc.
Page Two
June 16, 2000

          4.  All other provisions of the Agreement remain in full force and
effect.

If IFUE agrees to the foregoing, please sign where indicated below and return a
signed copy of this letter to me at the above address in New York. I will then
have GEM sign and return a fully executed copy to you.

Thank you,

Yours truly,

Ronald Scott Moss

AGREED AND ACCEPTED:

International Fuel Technology, Inc.         GEM Global Yield Fund Limited

By: /s/ William J. Lindenmayer              By: /s/ Pierce Loughran
    ----------------------------                ----------------------------
William J. Lindenmayer                      Name: Pierce Loughran
President                                   Title: Director<PAGE>   1

                                                                   EXHIBIT 10.6

                   FIFTH MODIFICATION TO AMENDED AND RESTATED
                      BUSINESS LOAN AND SECURITY AGREEMENT

       THIS FIFTH MODIFICATION TO AMENDED AND RESTATED BUSINESS LOAN AND
SECURITY AGREEMENT (this "Modification") is made as of the ____ day of April,
2000, by and among (i) BANK OF AMERICA, N.A., a national banking association (as
successor-in-interest to NationsBank, N.A.), acting in its capacity as a Lender
("Bank of America"), 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)
BANK OF AMERICA, N.A., a national banking association (as successor-in-interest
to NationsBank, N.A.), acting in its capacity as Agent for the Lenders, having
an office at 8300 Greensboro Drive, Suite 550, McLean, Virginia 22102; and (v)
BTG, INC., a Virginia corporation ("BTG"); BTG TECHNOLOGY SYSTEMS, INC., a
Virginia corporation; DELTA RESEARCH CORPORATION, a Virginia corporation;
CONCEPT AUTOMATION, INC. OF AMERICA, a Virginia corporation; NATIONS, INC., a
New Jersey corporation; STAC, INC., a Virginia corporation, all having principal
offices at 3877 Fairfax Ridge Road, 4B, Fairfax, Virginia 22030-7448; and each
other person or entity hereafter executing a "Joinder Agreement" pursuant to the
Loan Agreement (collectively, the "Borrowers"). 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 or modified, and as the same may be hereafter amended or
modified, the "Loan Agreement"), by and among the Agent, the Borrowers and the
Lenders (including Crestar Bank which is no longer a party thereto), 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 Fifty Million and No/100 Dollars ($50,000,000.00), but continues to
be evidenced by two (2) separate Replacement Revolving Promissory Notes (as
defined in EXHIBIT A hereto), in the aggregate maximum principal amount of
Ninety-five Million and No/100 Dollars ($95,000,000.00); and

       WHEREAS, the Loan is secured by, among other things, certain collateral
(the "Collateral") more fully described in Section 1 of Article III of the Loan
Agreement; and

       WHEREAS, pursuant to that certain Fourth Modification to Amended and
Restated Business Loan and Security Agreement dated January 26, 1999, by and
among the Agent, the Borrowers and Lenders, the Borrowers obtained a term loan
(the "Original Facility "B"") in the original aggregate principal amount of
Three Million Four Hundred Thousand and No/100 Dollars ($3,400,000.00), which
term loan was (a) made available to the Borrowers in addition to and not in
replacement of the existing revolving facility ("Facility "A""), (b) evidenced
by two (2) separate Term Promissory Notes (as defined in EXHIBIT A hereto), in
the original aggregate principal amount of Three Million Four Hundred Thousand
and No/100 Dollars ($3,400,000.00), and (c) secured by, among other things, the
Collateral; and
<PAGE>   2

       WHEREAS, the Term Promissory Notes which evidenced the Original Facility
"B" have been paid and satisfied in full; and

       WHEREAS, the Borrowers have requested that (a) the Agent and Lenders
consent to an asset acquisition (the "Acquisition") pursuant to which BTG will
acquire substantially all of the assets (the "SSDS Assets") of a division of
SSDS, Inc., a Colorado corporation ( "SSDS"); (b) the Lenders extend to the
Borrowers a new term loan ("Facility "B""), in the original aggregate principal
amount of Eight Million and No/100 Dollars ($8,000,000.00), the proceeds of
which shall be used to finance the Acquisition and certain costs and expenses
incurred in connection therewith; and (c) certain covenants set forth in the
Loan Agreement be modified; and

       WHEREAS, the Agent and Lenders have agreed to grant such consent, make
Facility "B" available to the Borrowers and modify certain covenants set forth
in the Loan Agreement, subject to the terms, covenants, conditions and
limitations set forth in this Modification, as hereinafter provided; and

       WHEREAS, the Lenders have also agreed to reallocate their Percentages of
the Commitment Amount and Loans among themselves such that, after giving effect
to such reallocation, Bank of America's Percentage shall be fifty-six percent
(56%) of the Commitment Amount (and Loans thereunder) and Fleet's Percentage
shall be forty-four percent (44%) of the Commitment Amount (and Loans
thereunder), 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 Agent, acting for and on behalf of the Lenders, hereby consents to
the Acquisition and agrees to make Facility "B" available to the Borrowers,
subject to the terms, conditions, covenants and limitations set forth in this
Modification.

       3. Simultaneously with the execution of this Modification, the proceeds
of Facility "B" shall be fully advanced to the Borrowers, and used solely for
the purpose of financing the purchase price for the Acquisition and other
amounts payable by BTG pursuant to that certain Asset Purchase Agreement dated
February 28, 2000, by and among BTG and SSDS (the "Asset Purchase Agreement"),
as well as the transactional costs and expenses incurred in connection with the
Acquisition. From and after the initial disbursement of the proceeds of Facility
"B", neither the Agent nor any Lender shall have any further obligation
whatsoever to advance or readvance the proceeds of Facility "B".

       4. Concurrent herewith, the Borrowers shall deliver to the Agent, in form
and substance reasonably satisfactory to the Agent (i) a fully executed Facility
"B" Term Promissory Note No. 1 (together with all extensions, renewals,
modifications and substitutions thereof or therefor, the "Bank of America
Facility "B" Note"), made by the Borrowers and payable to the order of Bank of
America in the original principal amount of Four Million Four Hundred Eighty

                                       2

<PAGE>   3

Thousand and No/100 Dollars ($4,480,000.00), (ii) a fully executed Facility "B"
Term Promissory Note No. 2 (together with all extensions, renewals,
modifications and substitutions thereof or therefor, the "Fleet Facility "B"
Note"), made by the Borrowers and payable to the order of Fleet in the original
principal amount of Three Million Five Hundred Twenty Thousand and No/100
Dollars ($3,520,000.00); (iii) a fully executed Second Modification to Ancillary
Loan Documents, pursuant to which the Borrowers shall acknowledge and agree that
all documents, instruments and agreements executed, issued and/or delivered in
connection with and securing the Loan, shall also secure Facility "B" and the
repayment of the Bank of America Facility "B" Note, the Fleet Facility "B" Note
and all extensions, renewals, modifications and substitutions thereof or
therefor (collectively, the "Facility "B" Notes"); (iv) duly adopted resolutions
of the respective Board of Directors of each Borrower, certified by a duly
authorized officer of each Borrower, authorizing the execution and delivery of
this Modification and all other documents, instruments and agreements described
herein and/or in connection herewith, and the performance by each Borrower of
its respective obligations contemplated hereby; (v) a fully executed copy of the
Asset Purchase Agreement; (vi) UCC search results, showing no liens, claims or
encumbrances filed against any of the SSDS Assets (other than Permitted Liens),
and (vii) evidence satisfactory to the Agent that on the date hereof, the
Maximum Borrowing Base exceeds the outstanding principal balance of the Loan by
at least Five Million and No/100 Dollars ($5,000,000.00). Within five (5)
Business Days of the date of this Modification, the Borrowers shall deliver to
the Agent an opinion of counsel, in form and substance reasonably satisfactory
to the Agent and each Lender, and issued by a law firm reasonably satisfactory
to the Agent; it being expressly understood and agreed that the Borrower's
failure to timely deliver said opinion of counsel as and when required hereby
shall constitute an Event of Default under the Loan.

       5. The definitions of "Facility "B"", "Facility "B" Commitment Amount"
and "Loan" set forth in the "Certain Definitions" section of the Loan Agreement
are hereby deleted in their entirety and the following substituted in lieu
thereof:

          ""FACILITY "B"" shall mean the term loan facility being extended
          pursuant to this Agreement, in the original aggregate principal amount
          of Eight Million and No/100 Dollars ($8,000,000).

          "FACILITY "B" COMMITMENT AMOUNT" shall mean Eight Million and No/100
          Dollars ($8,000,000).

          "LOAN" shall mean the loans made by the Lenders to the Borrowers
          pursuant to this Agreement in the Commitment Amount, or so much
          thereof as shall be advanced or readvanced from time to time, which
          are represented by the Facilities, and which shall be evidenced by,
          bear interest and be payable in accordance with the terms and
          provisions set forth in the Notes."

       6. The following definitions of "EBITDA", "Installment Note", "Mandatory
Net Cash Flow Payments" and "Net Cash Flow" are hereby added to the "Certain
Definitions" section of the Loan Agreement:

                                       3

<PAGE>   4

          ""EBITDA" shall mean, as of the date of any determination, the
          Borrowers' net income (or loss), plus interest expense, plus all
          charges against income for foreign, federal, state and local income
          taxes, plus depreciation expense, plus amortization expense, and
          excluding any other non-cash items to the extent included in
          determining net income (or loss), all as determined on a consolidated
          basis in accordance with GAAP.

          "INSTALLMENT NOTE" shall mean that certain Installment Note dated
          February 10, 1999, made by Government Technology Services, Inc., a
          Delaware corporation ("GTSI") and payable to the order of BTG, in the
          original principal amount of Two Million and No/100 Dollars
          ($2,000,000.00), together with all extensions, renewals, modifications
          and substitutions thereof approved by the Agent in writing.

          "MANDATORY NET CASH FLOW PAYMENTS" shall mean, as of any date of
          determination, any mandatory payment required to be paid pursuant to
          clause (a) of Section 5 of Article I of the Loan Agreement.

          "NET CASH FLOW" shall mean, for each quarterly period beginning with
          the quarter ending June 30, 2000, EBITDA for such period, minus
          (without duplication) the sum of interest expense, cash taxes paid,
          current payments of capitalized leases, capital expenditures,
          scheduled principal payments under the Facility "B" Notes and
          Mandatory Net Cash Flow Payments, in each case for such period and
          determined on a consolidated basis in accordance with GAAP."

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

          "5. ADDITIONAL MANDATORY PAYMENTS; REDUCTION OF COMMITMENT. In
          addition to all other sums payable by the Borrowers pursuant to any of
          the Notes, this Agreement or any other Loan Document, the Borrowers
          shall also make mandatory payments under the Facility "B" Notes, to be
          applied in inverse order of maturity under the Facility "B" Notes, in
          the amount of (a) fifty percent (50%) of Net Cash Flow; (b) one
          hundred percent (100%) of any and all payments made under the
          Installment Note; and (c) one hundred percent (100%) of the cash
          proceeds (net of reasonable and customary costs paid to unrelated and
          unaffiliated third parties in connection with the particular
          transaction) arising from the sale or disposition by BTG of the
          Installment Note or any capital stock of GTSI. Any mandatory payment
          required pursuant to clause (a) above shall be due and payable in full
          on or before the forty-fifth (45th) day following the close of each of
          the Borrowers' fiscal quarters, and any mandatory payment required
          pursuant to clauses (b) and/or (c) above shall be due and payable in
          full simultaneously with the occurrence of the event giving rise to
          such mandatory payment (i.e., a payment under the

                                       4

<PAGE>   5

          Installment Note, a sale or other disposition of the Installment Note,
          or a sale or other disposition of GTSI stock)."

       8. Section 3(c) of Article VI of the Loan Agreement is hereby deleted in
its entirety and the following substituted in lieu thereof:

          "(c) on or before the twentieth (20th) day following the close of each
          calendar month, the Borrowers will submit to the Agent and each Lender
          a Borrowing Base Certificate in the form of Exhibit 5 hereto, which
          certificate shall be certified by an authorized officer of the
          Borrowers and accompanied by a detailed current accounts receivable
          agings report;"

       9. 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:

 <TABLE>
 <CAPTION>
                                                                       REQUIRED TANGIBLE
                       PERIODS                                             NET WORTH
 -------------------------------------------------------------------------------------------------------------
 <S>                                                                   <C>
 From March 31, 2000 through June 29, 2000                             $12,000,000.00
 -------------------------------------------------------------------------------------------------------------
 From June 30, 2000 through September 29, 2000                         $13,500,000.00
 -------------------------------------------------------------------------------------------------------------
 From September 30, 2000 through December 30, 2000                     $15,500,000.00
 -------------------------------------------------------------------------------------------------------------
 From December 31, 2000 through March 30, 2000                         $17,500,000.00
 -------------------------------------------------------------------------------------------------------------
 From March 31, 2001 through June 29, 2001                             $19,500,000.00
 -------------------------------------------------------------------------------------------------------------
 From June 30, 2001 through the Maturity Date                          19,500,000.00, plus 67% of net income
                                                                       (as determined on a consolidated basis
                                                                       in accordance with GAAP at the end
                                                                       of each fiscal quarter).
 -------------------------------------------------------------------------------------------------------------
 </TABLE>

          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."

                                       5
<PAGE>   6

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

          "(c) Funded Debt to Consolidated EBITDA Ratio. The Borrowers, on a
          consolidated basis, will maintain at all times during the following
          periods, a ratio of Funded Debt to Consolidated EBITDA which is not
          greater than the ratio set forth below:

<TABLE>
<CAPTION>
-----------------------------------------------------------------------------------------
                    FOR THE FISCAL                                          MAXIMUM
                    QUARTER ENDED                                            RATIO
-----------------------------------------------------------------------------------------
<S>                                                                     <C>
                    March 31, 2000                                       4.50 to 1.00
-----------------------------------------------------------------------------------------
                    June 30, 2000                                        4.50 to 1.00
-----------------------------------------------------------------------------------------
                  September 30, 2000                                     4.50 to 1.00
-----------------------------------------------------------------------------------------
                  December 31, 2000                                      4.50 to 1.00
-----------------------------------------------------------------------------------------
March 31, 2001 and each fiscal quarter end thereafter                    4.00 to 1.00
-----------------------------------------------------------------------------------------
</TABLE>

          For purposes hereof, (i) "Funded Debt" shall mean the outstanding
          principal balance of borrowed funds pursuant to this Agreement
          (including, without limitation, the face amount of outstanding Letters
          of Credit), plus all other interest bearing obligations of the
          Borrowers as of the date of determination; and (ii) "Consolidated
          EBITDA" shall mean as of the date of the particular determination,
          EBITDA calculated on a consolidated basis in accordance with GAAP,
          excluding all non-operating results (including, but not limited to,
          the profit or loss from the sale of the GTSI Stock). Consolidated
          EBITDA shall be calculated as of each fiscal quarter end on a rolling
          four (4) quarter basis.

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

          "(d) Maintenance of Fixed Charge Coverage. The Borrowers shall not
          permit the ratio of (i) Consolidated EBITDA of the Borrowers, to (ii)
          Consolidated Fixed Charges, measured as of each date set forth below
          for the period of four (4) consecutive full fiscal quarters of the
          Borrowers ended on such date, to be less than the ratio set forth
          below:

<TABLE>
<CAPTION>
------------------------------------------------------------------------------------
                    FISCAL QUARTER ENDED                             MINIMUM RATIO
------------------------------------------------------------------------------------
<S>                                                                 <C>
                      March 31, 2000                                 1.50 to 1.00
------------------------------------------------------------------------------------
                      June 30, 2000                                  1.30 to 1.00
------------------------------------------------------------------------------------
                    September 30, 2000                               1.30 to 1.00
------------------------------------------------------------------------------------
                    December 31, 2000                                1.30 to 1.00
------------------------------------------------------------------------------------
         March 31, 2001 and the last day of each                     1.40 to 1.00
                 fiscal quarter thereafter
------------------------------------------------------------------------------------
</TABLE>

       12. The second sentence set forth in Section 8 of Article VII of the Loan
Agreement is hereby deleted in its entirety and the following substituted in
lieu thereof:

                                       6
<PAGE>   7

          "Notwithstanding the foregoing, it is understood and agreed that (a)
          in the absence of any Event of Default and so long as no act, event or
          condition exists which with notice or the passage of time, or both,
          would constitute an Event of Default, BTG may repurchase the dollar
          equivalent of its capital stock (determined as of the date of any such
          repurchase), provided that the aggregate amount of all such
          repurchases subsequent to March 31, 1999 shall not exceed Two Million
          and No/100 Dollars ($2,000,000.00), (b) payments made by any Borrower
          to Resources pursuant to Section 15 of Article V of this Agreement
          shall not violate the negative covenant set forth in this Section 8 of
          Article VII of this Agreement; and (c) in the absence of any Event of
          Default and so long as no act, event or condition exists which with
          notice or the passage of time, or both, would constitute an Event of
          Default, any payments, loans or advances made by any Borrower to or
          for the benefit of Edutest, Inc., a Virginia corporation ("Edutest"),
          shall not violate the negative covenant set forth in this Section 8 of
          Article VII of this Agreement; provided that the aggregate amount of
          any and all such payments, loans and/or advances to or for the benefit
          of Edutest does not, at any time, exceed Two Hundred Fifty Thousand
          and No/100 Dollars ($250,000.00);"

       13. BTG hereby represents and warrants to the Agent and the Lenders that
(a) all of the SSDS Assets are free and clear of any and all liens, claims and
encumbrances (other than Permitted Liens); (b) all of the SSDS Assets
constituting accounts, accounts receivable and books and records (as such terms
may be defined in the Virginia Uniform Commercial Code) will be located at BTG's
address set forth in the Preamble to this Modification, and all other SSDS
Assets will be located at one or more of the locations set forth on SCHEDULE 1
attached to this Modification; and (c) immediately following the Acquisition,
the Agent (for the ratable benefit of the Lenders) shall have a valid and
perfected first priority security interest in and to all of the SSDS Assets
(without further documentation) pursuant to (i) the Loan Agreement and the UCC
Financing Statements previously executed by BTG and the other Borrowers and
filed among the public records of Fairfax County, Virginia and with the Virginia
State Corporation Commission in connection with the Loan, and (ii) UCC Financing
Statements to be executed by BTG on the date hereof and filed in the appropriate
jurisdiction necessary to perfect a security interest in and to the SSDS Assets.

       14. The Lenders and Borrowers hereby acknowledge and confirm that the
percentage interests in the Loan and Loan Commitments of Bank of America and
Fleet shall be as set forth in SCHEDULE 2 attached to this Modification. With
respect to the existing Facility "A" Notes, the Borrowers, Agent and Lenders
acknowledge and agree that (a) the maximum principal amount of the Bank of
America Facility "A" Note shall be increased from Fifty-three Million One
Hundred Twenty-five Thousand and No/100 Dollars ($53,125,000.00) to Fifty-three
Million Two Hundred Thousand and No/100 Dollars ($53,200,000.00); and (b) the
maximum principal amount of the Fleet Facility "A" Note shall be reduced from
Forty-one Million Eight Hundred Seventy-five Thousand and No/100 Dollars
($41,875,000.00) to Forty-one Million Eight Hundred Thousand and No/100 Dollars
($41,800,000.00). The foregoing adjustments between the Facility "A" Notes shall
be (i) accomplished by Bank of America advancing, under the Bank

                                       7

<PAGE>   8

of America Facility "A" Note, an amount equal to .0789474% of the current
outstanding principal balance of the Fleet Facility "A" Note and paying such
amounts to Fleet, thereby reducing the outstanding principal balance of the
Fleet Facility "A" Note by such amount, and (ii) evidenced by a certain Allonge
and Second Modification to Replacement Revolving Promissory Note No. 1 and a
certain Allonge and Second Modification to Replacement Revolving Promissory Note
No. 2, each of which shall be (x) dated the date hereof, (y) in form and
substance satisfactory to the Agent and Lenders in all respect, and (z) executed
and delivered by the Borrowers to the Agent simultaneously with the Borrowers'
execution and delivery of this Modification.

       15. The Borrowers acknowledge and agree that the Asset Purchase Agreement
shall not be altered, modified or amended in any respect without the Agent's
prior written consent.

       16. In consideration of the transactions contemplated by this
Modification, the Borrowers shall pay to the Agent, for the benefit of the
Lenders (pro rata based on each Lender's Percentage), a modification fee in the
amount of One Hundred Thousand and No/100 Dollars ($100,000.00), which fee shall
be paid in cash on or before the date of this Modification. The Borrowers shall
also 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.

       17. 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 and its obligations hereunder (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.

       18. 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.

       19. 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]

                                       8

<PAGE>   9

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

<TABLE>
<CAPTION>
                                                                   BORROWERS:
                                                                   ----------
<S>                                                    <C>
[Corporate Seal]                                       BTG, INC., a Virginia corporation
ATTEST:

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

[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
</TABLE>

                  [Signatures Continued on the Following Page]

                                       9

<PAGE>   10

<TABLE>
<S>                                                    <C>
[Corporate Seal]                                       STAC, INC., a Virginia corporation
ATTEST:

By: /s/ Deborah Fox                                    By: /s/ Edward H. Bersoff
    ------------------------------                         ----------------------------------
Name:   Deborah Fox                                    Name:   Edward H. Bersoff
Title:  Secretary                                      Title:  CEO

                                                       AGENT:
                                                       -----

                                                       BANK OF AMERICA, N.A., a national banking
                                                       association (as successor-in-interest to
                                                       NationsBank, N.A.), acting in its capacity as
                                                       Agent

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

                                                       LENDER(S):
                                                       ---------
                                                       BANK OF AMERICA, N.A., a national banking
                                                       association (as successor-in-interest to
                                                       NationsBank, N.A.), acting in its capacity as
                                                       Lender

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

                                                       FLEET CAPITAL CORPORATION, a
                                                       Rhode Island corporation

                                                       By: /s/ Dennis S. Losin
                                                           ----------------------------------
                                                       Name:   Dennis S. Losin
                                                       Title:  Vice President
</TABLE>

                                       10

<PAGE>   11

                                    EXHIBIT A

For purposes of this Modification, the following terms shall have the following
meanings:

"Replacement Revolving Promissory Notes" shall mean each and all of the
promissory notes executed, issued and delivered pursuant to the Loan Agreement
in connection with Facility "A", together with all extensions, renewals,
modifications and substitutions thereof and therefor.

"Term Promissory Notes" shall mean each and all of the promissory notes
executed, issued and delivered pursuant to the Loan Agreement in connection with
the Original Facility "B".

<PAGE>   12

                                   SCHEDULE 1

                             [SSDS Asset Locations]

                                       2
<PAGE>   13

                                   SCHEDULE 2
<TABLE>
<CAPTION>
           Lenders                                         Percentage
           -------                                         ----------
<S>                                                        <C>
  Bank of America, N.A.                                        56%
  8300 Greensboro Drive
  Suite 550
  McLean, Virginia  22102
  Tel. (703) 761-8108
  Fax. (703) 761-8344

  Fleet Capital Corporation                                    44%
  300 Galleria Pkwy. Northwest
  Suite 800
  Atlanta, Georgia  30339
  Tel. (770) 859-2400
  Fax. (770) 859-2483
</TABLE>

                                       3

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