A proposal to expand Fairfax County's Mount Vernon Community Park into a $6 million recreation complex will be the subject of a public hearing at 8 p.m. July 30 at Riverside Elementary School at 8410 Old Mount Vernon Road.

The park, on Old Mount Vernon Road in southeast Fairfax County, now is undeveloped except for some tennis courts.

Preliminary plans call for expanding the park into a smaller version of the county's popular Wakefield Recreation Center. The proposal, as outlined by the Fairfax County Park Authority, includes an indoor swimming pool, handball courts, recreation rooms, saunas, community rooms, a snack bar and parking for 290 cars.

A private consulting firm recommended last year that the recreation complex provide an indoor swimming pool near Mount Vernon High School. The park is opposite the high school and near Riverside Elementary and Walt Whitman Intermediate schools.

The Park Authority is purchasing 9.3 acress to add to the 17-acre park and building a new entrance on Nalls Road. The pool and recreation center would be built largely on the additional acreage, which is vacant except for an abandoned house, according to Edward Nenstiel, landscape architect for the park authority.

The county has no money to develop the park, but the pool and recreation center could be built by 1984 or 1985 if funding is included as part of a park bond issue expected to go before voters in 1982, Nenstiel said.

It is estimated the recreation center would cost about $650,000 a year to operate. Nenstiel said, but user fees should cover all operating costs.

The park authority is now completing a second county recreation complex, at Lee District Park on Telegraph Road, and a new indoor pool is expected to open this winter at the Mount Vernon Ice Rink in the northern part of the Mount Vernon District. Another center, at Providence District Park at the Beltway and Rte. 50, is in the planning stages.

Copies of the flyer on the proposed new master plan for Mount Vernon Community Park are available by calling the county park authority at 941-5000, ext. 261. Detailed preliminary plans are available at park authority headquarters on Hummer Road or the county library at 2501 Sherwood Hall La.