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                                                                    EXHIBIT 10.9

                             FOURTH AMENDMENT TO THE
                        MANTECH INTERNATIONAL 401(k) PLAN

         AMENDMENT to the ManTech International 401(k) Plan (the "Plan") by
ManTech International Corporation (the "Company").

         The Company maintains the Plan, effective as of January 1, 1993, and
amended and restated effective as of October 1, 1998. The Company has the power
to amend the Plan and now wishes to do so. Unless otherwise provided herein, the
amendment shall be effective as of October 1, 1998.

         NOW THEREFORE, the Plan is amended as follows:

I.       Section 1.15 of the Plan is amended by replacing the reference to "2.7
         (b)" with "2.1(b)."

II.      Sections 3.10 and 4.2(a)(iii) of the Plan are amended by replacing all
         references to "4.2(a)(iv)" with "4.2(a)(iii)."

III.     The portion of Section 4.5(b) of the Plan preceding Section 4.5(b)(i)
         is amended in its entirety to read as follows:

         If the Annual Addition to a Participant's Account in any Limitation
         Year exceeds the limitation of this Section due to allocation of
         forfeitures, a reasonable error in estimating a Participant's
         Compensation or a reasonable error in determining the amount of
         Deferral Contributions that may be made with respect to any individual
         under the limits of Code section 415 or under other limited facts and
         circumstances approved of by the Commissioner of the Internal Revenue
         Service, then the amounts that would have been credited to his Account
         but for this Section in excess of the limitation shall be administered
         as follows:

IV.      Section 4.7(a) of the Plan is amended in its entirety to read as
         follows:

         (a)  Effective for Plan Years beginning after December 31, 1996, each
              Plan Year, the Actual Deferral Percentage of eligible Highly
              Compensated Employees shall not exceed the greater of:

               (i)  The Actual Deferral Percentage of all other eligible
                    Employees for the preceding Plan Year multiplied by 1.25; or

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                    (ii) The lesser of the Actual Deferral Percentage of all
                         other eligible Employees for the preceding Plan Year
                         multiplied by 2, or the Actual Deferral Percentage of
                         all other eligible Employees for the preceding Plan
                         Year plus 2 percentage points.

V.       Section 4.8(a) of the Plan is amended in its entirety to read as
         follows:

         (a)        Effective for Plan Years beginning after December 31, 1996,
                    each Plan Year, the Contribution Percentage of eligible
                    Highly Compensated Employees shall not exceed the greater
                    of:

                    (i)  The Contribution Percentage of all other eligible
                         Employees for the preceding Plan Year multiplied by
                         1.25; or

                    (ii) The lesser of the Contribution Percentage of all
                         other eligible Employees for the preceding Plan Year
                         multiplied by 2, or the Contribution Percentage of
                         all other eligible Employees for the preceding Plan
                         Year plus 2 percentage points.

VI.      Section 4.8(c) of the Plan is amended by adding the following new
         Section 4.8(c)(vi):

         To the extent Deferral Contributions or Participant Basic After-Tax
         Contributions are distributed to a Participant under Section 4.9,
         Company Basic Matching Contributions attributable to such Deferral
         Contributions or Participant Basic After-Tax Contributions shall be
         forfeited as of the end of the Plan Year in which the contributions
         were made, and shall be used to reduce future Company Contributions.

VII.     Effective for Plan Years beginning after December 31, 1996, the second
         and third sentences of Section 4.8(e) of the Plan are amended in their
         entirety to read as follows:

         If the aggregate limit is exceeded, the Excess Contributions and the
         Excess Aggregate Contributions of Highly Compensated Employees (as
         defined in Section 4.9(b)) will be calculated and distributed as
         provided in Section 4.9(b) of the Plan. The amount of distributions
         under this Section shall be determined using the dollar leveling method
         described in Section 4.9(e).

VIII.    Effective for Plan Years beginning after December 31, 1996, Section
         4.9(b) of the Plan is amended in its entirety to read as follows:

         For purposes of this Section, "Excess Contributions" means, for a Plan
         Year, the excess of the Actual Deferral Percentage of Highly
         Compensated Employees over the maximum Actual Deferral Percentage for
         Highly Compensated Employees permitted under the anti-discrimination
         tests described in Section 4.7 (determined by reducing deferrals made
         by

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         Highly Compensated Employees in the order of their Deferral Percentages
         beginning with the highest of such percentages). For purposes of this
         Section, "Excess Aggregate Contributions" means, for a Plan Year, the
         excess of the Contribution Percentages of Highly Compensated Employees
         over the maximum Contribution Percentage for Highly Compensated
         Employees permitted under the anti-discrimination tests described in
         Section 4.8 (determined by reducing contributions made on behalf of
         Highly Compensated Employees in order of their Contribution Percentages
         beginning with the highest of such percentages). Any Excess
         Contributions and any Excess Aggregate Contributions and income
         attributable to those contributions shall be distributed to the Highly
         Compensated Employees within 2 1/2 months after the close of the Plan
         Year in which the Deferral Contributions, Participant Voluntary
         Contributions, and Company Contributions were made. In determining the
         amount of the distributions under this Section, the Plan Administrator
         shall use the dollar leveling method described in subsection (e).

IX.      Effective for Plan Years beginning after December 31, 1996, Section
         4.9(e) of the Plan is amended in its entirety to read as follows:

         The dollar leveling method of reducing an Employee's Excess
         Contributions means the method of reducing Excess Contributions
         starting with the Highly Compensated Employee with the greatest dollar
         amount of Deferral Contributions and continuing until the amount of
         Excess Contributions has been accounted for. The dollar leveling method
         of reducing an Employee's Excess Aggregate Contributions means the
         method of reducing Excess Aggregate Contributions starting with the
         Highly Compensated Employee with the greatest dollar amount of
         Voluntary Contributions and Company Contributions and continuing until
         the amount of Excess Aggregate Contributions has been accounted for.

X.       Section 4.9(f) of the Plan is amended in its entirety to read as
         follows:

         The amount of Deferral Contributions to be distributed pursuant to this
         section shall be coordinated with the amount of Excess Contributions to
         be distributed as determined under Section 4.7 as follows: first, the
         amount of Deferral Contributions to be distributed shall be reduced by
         the amount of Excess Contributions previously distributed or
         re-characterized for the Plan Year beginning in such taxable year; and
         second, the amount of Excess Contributions to be distributed shall be
         reduced by Deferral Contributions which were previously distributed for
         the taxable year ending in the same Plan Year.

XI.      Section 6.4(a) of the Plan is amended in its entirety to read as
         follows:

         If a Participant dies before his vested interest in his Account has
         begun to be distributed, the Participant's vested interest in his
         Account will be paid to the Participant's Beneficiary in a single sum
         cash payment or in a form selected pursuant to Section 6.8, unless a
         survivor annuity is automatically payable pursuant to subsection (b)
         below or Section

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         6.8(a). If a Participant dies while receiving distributions from the
         Plan, the balance of the Participant's vested interest in his Account
         shall be paid to the Participant's Beneficiary at least as rapidly as
         under the method of payment being used under Section 6.8 as of the date
         of the Participant's death.

XII.     The third sentence of the second paragraph of Section 6.7(c) of the
         Plan is amended in its entirety to read as follows:

         Distributions under this Section shall be made in accordance with Code
         section 401(a)(9) and any regulations thereunder, including the minimum
         distribution incidental benefit requirements of section 1.401(a)(9)-2
         of the proposed Treasury regulations.

XIII.    In all respects not amended, the Plan is hereby ratified and confirmed.

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         To record adoption of the Amendment as set forth above, ,the Company
has caused this document to be signed on this ____ day of ____________________.

                                               MANTECH INTERNATIONAL CORPORATION

                                               BY: _____________________________

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