<PAGE>

                                                                    EXHIBIT 10.3




                  AMENDMENT TO MORTGAGE, SECURITY AGREEMENT,
                                AND ASSIGNMENT


     This Amendment to Mortgage, Security Agreement and Assignment is made as of
the 12th day of June, 2000 by and between DYNAMICS RESEARCH CORPORATION
(hereinafter, the "Mortgagor"), a Massachusetts corporation with an office at 60
Frontage Road, Andover, Massachusetts and FAMILY BANK, FSB, now known as FIRST
MASSACHUSETTS BANK, N.A., a national banking association, for itself and as
collateral agent for the benefit of each of the lenders under a certain Loan and
Security Agreement dated as of February 10, 2000  (hereinafter, the "Mortgagee")
having an address for purposes hereof at 153 Merrimack Street, Haverhill,
Massachusetts, in consideration of the mutual covenants contained herein and the
benefits to be derived herefrom.

     WHEREAS, the Mortgagor granted to the Mortgagee a certain Mortgage,
Security Agreement and Assignment (hereinafter, the "Mortgage") in and to
certain  premises located on Frontage Road, Andover, Massachusetts (as more
particularly described in the Mortgage, the "Premises") dated February 10, 2000
and recorded with the Essex County Registry of Deeds at Book 5676, Page 217 to
                                                             ----       ---
secure the Mortgagor's prompt, punctual and faithful payment and performance of
certain of the Mortgagor's present and future Liabilities (as defined in the
Mortgage).

     WHEREAS, the Mortgagor and the Mortgagee wish to amend, modify and
supplement the Mortgage to secure an amendment and increase of the Mortgagor's
existing Liabilities to the Mortgagee to be included as part of the Liabilities
secured by said Mortgage, all as more particularly hereinafter set forth;

     NOW THEREFORE, in consideration of the above premises and of the sum of One
Dollar ($1.00) and other good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, the Mortgagor and the Mortgagee
hereby covenant and agree as follows:

     1.   The following text appearing in Article 1, clause (iii) and (iv) of
          the Mortgage is hereby deleted:

          "(iii) a certain Term Note of even date made by, among others, the
          Mortgagor payable to Family Bank, FSB in the original principal amount
          of $2,500,000.00, and (iv) a certain Term Note made by, among others,
          the Mortgagor payable to Brown Brothers Harriman & Co. in the original
          principal amount of $5,000,000.00, and any extensions, renewals,
          substitutions, modifications, or  replacements of any of the foregoing
          (hereinafter, singly and collectively, the "Notes"),"

and is hereby replaced with the following:

          "(iii) a certain Amended and Restated Term Note dated as of June 12th,
          2000 made by, among others, the Mortgagor payable to First
          Massachusetts Bank, N.A., formerly known as Family Bank, FSB in the
          original principal amount of $5,000,000.00, and (iv) a certain Amended
          and Restated Term Note dated as of June 12th, 2000 made by, among
          others, the Mortgagor payable to Brown Brothers Harriman & Co. in the
          original principal amount of $5,000,000.00, and any extensions,
          renewals, substitutions, modifications or replacements of any of the
          foregoing (hereinafter, singly and collectively, the "Notes"),"

     2.   Except as specifically modified herein, all terms and conditions of
          the Mortgage shall remain in full force and effect and are hereby
          ratified and confirmed.  The Mortgage, as modified hereby, and as
          provided in said
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          Mortgage, is upon the STATUTORY CONDITION and upon the further
          condition that all covenants and agreements of the Mortgagor contained
          therein and herein shall be kept and fully performed, for any breach
          of which condition the holder hereof shall have the STATUTORY POWER OF
          SALE.

     3.   The Mortgagor acknowledges, confirms and agrees that as of the date
          hereof it has no offsets, defenses, claims or counterclaims against
          the Mortgagee with respect to any of its liabilities or obligations
          due and owing to the Mortgagee, and, to the extent that the Mortgagor
          has or  has ever had any such offsets, defenses, claims or
          counterclaims, the Mortgagor hereby specifically WAIVES and RELEASES
          any and all rights to such offsets, defenses, claims or counterclaims.



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                                      -2-
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     IN WITNESS WHEREOF, the parties hereto have caused these presents to be
signed, sealed and acknowledged and duly authorized as of the  12th day of June,
                                                               --
2000.

                                    DYNAMICS RESEARCH CORPORATION
                                    ("Mortgagor")


                                    By: /s/ David Keleher
                                        ------------------
                                        David Keleher, Vice President of Finance
                                        and Chief Financial Officer

                                    By: /s/ David C. Proctor
                                        --------------------
                                        David C. Proctor, Treasurer

                                    ("Mortgagee")

                                    FIRST MASSACHUSETTS BANK, N.A., formerly
                                    known as FAMILY BANK, FSB, for itself and as
                                    collateral agent

                                    By:     /s/  C. Lee Willingham
                                            ----------------------

                                    Name:   C. Lee Willingham
                                            -----------------
                                    Title:  Vice President
                                            --------------


                         COMMONWEALTH OF MASSACHUSETTS

Essex County, ss.                                                  June 12, 2000
----------------                                                        --

     Then personally appeared the above named David Keleher and David C.
Proctor, being the President and Treasurer of Dynamics Research Corporation, and
acknowledged the foregoing instrument to be their free act and deed and the free
act and deed of said corporation, before me,


                                       /s/ Dawn Murphy Scanlon
                                       -----------------------
                                       Notary Public
                                       My Commission Expires:  7/30/2004
                                                               ---------


                         COMMONWEALTH OF MASSACHUSETTS

Middlesex, ss.                                                     June __, 2000
--------------

     Then personally appeared the above named C. Lee Willingham, the Vice
President of First Massachusetts Bank, N.A., formerly known as Family Bank, FSB,
and acknowledged the foregoing instrument to be said person's free act and deed
and the free act and deed of said entity, before me,


                                       ______________________________
                                       Notary Public
                                       My Commission Expires:_________