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                                                                       EX. 10.18

                      SECOND AMENDMENT TO LEASE AGREEMENT

      THIS SECOND AMENDMENT TO LEASE AGREEMENT (this "SECOND AMENDMENT") is made
and entered into as of the 11th day of May, 2001, by and between BUILDING VII
ASSOCIATES L.C., a Virginia limited liability company formerly known as Building
VI Associates L.C. ("LANDLORD"), and PEC SOLUTIONS, INC., a Delaware corporation
("TENANT").

                                   RECITALS:

      A. Landlord and Tenant entered into that certain Office Lease Agreement
dated February 5, 2001, amended by First Amendment to Lease Agreement dated May
7, 2001 (the "LEASE"), whereby Landlord leased to Tenant and Tenant leased from
Landlord the Premises (as defined in the Lease).

      B. Except as otherwise provided herein to the contrary, all capitalized
terms used in this Amendment shall have the same meanings as are attributed
thereto in the Lease.

      C. Landlord and Tenant desire to amend the Lease as more fully described
in this Amendment.

      NOW, THEREFORE, in consideration of the mutual covenants and agreements
set forth herein and of other good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, Landlord and Tenant, intending
legally to be bound, hereby agree as follows:

      1. The name of Landlord was changed from Building VI Associates L.C. to
BUILDING VII ASSOCIATES L.C., effective May 11, 2001. All references to Landlord
in the Lease shall hereinafter reflect such name change and shall be demed to
refer to Building VII Associates L.C.

      2. Except as modified in this Amendment, the Lease remains unmodified and
in full force and effect.


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      IN WITNESS WHEREOF, Landlord and Tenant have caused this Amendment to be
signed and sealed by their duly authorized signatories under seal as of the day
and year first above written.

                                  LANDLORD:

                                  BUILDING VII ASSOCIATES L.C.
                                  Formerly known as Building VI Associates L.C.

                                  By:                            (SEAL)
                                         -----------------------
                                  Name:
                                         -------------------------------
                                  Title:
                                         -------------------------------


                                  TENANT:

                                  PEC SOLUTIONS, INC.

                                  By:                            (SEAL)
                                         -----------------------
                                  Name:
                                         -------------------------------
                                  Title:
                                         -------------------------------


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