Expanding Metrorail station service generally enhances already vibrant commercial locations, but has not proved to be a panacea for marginal sites, according to area real estate professionals.

New construction has boomed near Metro stations at Connecticut and L streets NW, Rosslyn, Crystal City, Van Ness and Friendship Heights, but those locations were doing well in term of development and commercial use before the arrival of the rapid transit service.

Although Metrorail service as started in 1976, the number of riders has increased as the price of gasoline has risen. In the suburbs especially, Metro's impact on residential construction has become apparent. Locations near Metro stops attract redevelopers and spur construction of town houses and condominium apartments.

Kenneth J. Luchs, president of the Washington Board of Realtors, said the new rapid transit system, like the Capital Beltway, is both huge in concept and long in completion. "But I'm convinced that there are opportunities for investment around key locations with rewards that are worth the patience involved," Luchs said.

An example of confidence in the value of Metrorail service is the 35-acre Mount Eagle site on Rte. 1, south of I-495 in Fairfax County, where International Developers Inc. plans to build four high-rise units of 1,000 condominium apartments. Developer Giuseppe Cecchi says he will offer bus service to the Huntington Metro station, scheduled to open in early 1982.

In downtown Washington, developer Gerald Miller built a red-brick office building with prime commercial space on leased air rights over the Farragut West station at the northeast corners of Connecticut and L NW. The office space in the building, designed by Skidmore, Owings and Merrill, was leased before construction was completed. New commercial space commands some of the highest leases in downtown.

On the southwest corner of that intersection, developers Ted Lerner and Albert (Sonny) Abramson plan to raze the old LaSalle building and nearby properties to provide a site for Washington Square. With at least 700,000 square feet of space, the structure will be a combination of office and commercial space highlighted by an atrium over the Metro access. The architect is Chloethiel Smith.

Another major project is being planned above the Bethesda Metro station, at the intersections of East-West Highway, Wisconsin Avenue and Old Georgetown Road, which is scheduled to open late in 1983. Henry Cord, chief property manager for Metro, said that a complex of 640,000 square feet of hotel, commercial and office space is slated for the Metro station area. On an adjacent site, Clark Enterprises Inc. is planning a major high-rise complex that will have condominium apartments and office and commercial space.

A 630,000 square foot office complex called Capital Gallery is under construction in a District urban renewal block at 6th and 7th street SW at Maryland Avenue. Esacalators will lead to the ground level L'Enfant Plaza Metro Station in front of the $24 million complex, which is being developed by Boston Properties Inc. and being built by George Hyman Construction Co. The architectural firm is Gruen Associates.

Meanwhile, the Washington Metropolitan Area Transit Authority has asked for bids to develop 17,700 square feet of ground over a downtown station access on the southwest corner of 14th and I streets NW. Another parcel of 19,935 square feet is available for bids at the Takoma Park station between Cedar and Vine streets. Zoning is C-2-A.