EXHIBIT 99.1

                CERTIFICATION PURSUANT TO 18 U.S.C. SECTION 1350,
                             AS ADOPTED PURSUANT TO
                  SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002

In connection with the ManTech International Corporation (the "Company")
Quarterly Report on Form 10-Q for the period ending June 30, 2002 as filed with
the Securities and Exchange Commission on the date hereof (the "Report), I,
George J. Pedersen, Chief Executive Officer of the Company, certify pursuant to
18 U.S.C. Section 1350, as adopted pursuant to Section 906 of the Sarbanes-Oxley
Act of 2002, to the best of my knowledge, that:

         (1)   The Report fully complies with the requirements of Section 13(a)
                or 15(d) of the Securities Exchange Act of 1934, as amended; and

         (2)   The information contained in the Report fairly presents, in all
               material respects, the financial condition and results of
               operations of the Company.

This certificate is being made for the exclusive purpose of compliance by the
Chief Executive Officer of the Company with the requirements of Section 906 of
the Sarbanes-Oxley Act of 2002, and may not be disclosed, distributed or used
by any person or for any reason other than as specifically required by law.


Date:_________________________                       By:________________________

                                                     George J. Pedersen
                                                     Chief Executive Officer

                                       20