Fairfax County officials, worried that their jurisdiction may lose two new seats in Virginia's House of Delegates, yesterday said they will join a court fight in support of a reapportionment plan that grants Fairfax increased representation.

The action should make Fairfax one of 10 parties involved in a complex lawsuit over the plan, which is being challenged on grounds that it violates constitutional guarantees of equal representation and is racially discriminatory.

The plan, approved by the General Assembly last spring, grants Fairfax 12 delegates, two more than the county currently has. With legal challenges to the new plan threatening to delay the scheduled fall legislative elections, several parties in the lawsuit are urging that the present apportionment plan be kept in place until the issue is settled.

Fairfax officials maintained that keeping the old plan would shortchange citizens in rapidly growing areas of the state and grant too much representation in areas, such as Norfolk, that are losing population.

District Judge D. Dortch Warriner heard arguments on the issue earlier this week in Richmond, but did not indicate when he would make a decision. State officials have warned that the matter must be settled by July 2 if the scheduled Nov. 3 legislative elections are to be held as planned.