The Fairfax County Board of Supervisors yesterday voted 6 to 3 to recommend that Metro extend its subway service to Vienna as was planned in the original 100-mile Metro system.

However, the board did not rule out building, a future station at Tysons Corner, a location some supervisors felt would be a better Metro station site.

The board also decided to seek federal funds to acquire land for a Tysons Corner station that would be a link in an eventual subway line to federally owned Dulles International Airport.

The Fairfax board's decision on the Vienna line is likely to weigh heavily in decisions made by Metro's Policy Steering Committee, which will vote Wednesday on the configuration of a regional subway system.

At the request of the Senate and The Transportation Department, the steering committee began a year ago to study alternatives to construction the four uncompleted lines of the approved 100-mile system, including the one to Vienna.The Senate and Transportation Department had become alarmed that the construction cost of Metro had risen 100 percent above original estimates 10 year ago.

Supervisor Joseph Alexander (D-Lee), the Fairfax board's representative to the Metro board, said the Vienna choice was "crucially significant."

"Deciding on the Vienna line gives Fairfax County the best guarantee it has ever had that it will get Metro-rail lines in the county at all," Alexander said. "This decision closes the phase of looking at alternatives and getting into the real decision-making process."

He said the delay and increased cost of building a Tyson' Corner station could easily "throw that line out of the race altogether" when detailed financial studies on building the subway lines begin in August.

"With the Vienna station we have a much better chance," he said.

Fairfax Transportation Director Shiva Pant said the cost of building the subway from the scheduled Ballston station in Arlington westward to Tysons Corner would cost $328 million over four years compared to 269 million for a line to Vienna, a $59 million difference.

The Tysons Corner station also would take about five years longer to build than the Vienna station, which is scheduled to be open by mid-1982.

Supervisors John P. Shacochis (R-Dranssville), Martha V. Pennino (D-Centreville) and Audrey Moore (D-Annandale), who voted against the Vienna station, urged the board to look at the long-range effects of building a Tysons Corner station.They claimed that Tysons Corners' high-density development and business potential could support a subway station better than the less-developed and more residential Vienna area.

As proposed, the Vienna line will include stops at East Falls Church, on Rtes. 29-211 near the Fairfax County-Arlington border; at West Falls Church, on Rte. 7 near George Mason High School, and at Dunn Loring, near the intersection of Interstate Rte. 66 and the Capital Beltway.

Although the town of Vienna opposes a Vienna station, both Arlington and Falls Church support it, a factor that may prevent some of the interjurisdictional squabbling that has beset previous debates on where to build subway lines.

The supervisors also voted to recommend that Metro extend a subway line from Alexandria to Franconia in the county, rather than stop in Alexandria as the city council wanted.