Metro will hold a public hearing next Wednesday, March 4, on plans to extend the subway's Yellow Line from Alexandria to the Franconia-Springfield area. But the possibility of carrying out those plans was severely crippled last week when the Reagan administration announced that it may oppose use of federal funds to complete the Washington-area subway system.

The hearing will be at 7:30 p.m. at Forestdale Elementary School, 6530 Elder Ave., Springfield. Written comments on the plans may be sent to Metro within five days after the hearing.

Before last week's announcement, the federal government had agreed to pay 80 percent of the cost -- now estimated to be $8.2 billion -- for the full 101-mile Washington-area subway system. About half of the system, including the proposed Franconia-Springfield line, remains to be funded.

Under current plans, the Franconia-Springfield station, scheduled to open in 1986, would be the last stop on Virginia's Yellow Line which will split from the Blue Line at the King Street station in southern Alexandria. Metro has estimated that about 24,000 riders a day would use the Franconia-Springfield station. Metro originally had proposed two additional stations for the area, one at the Beltway and another inside the Beltway at a spur to Backlick Road. Fairfax County officials, however, urged adoption of the current plan for one station, although a Beltway stop and/or extensions could be built later, according to Metro officials.

Under current plans, the route would be an above-ground line along the Richmond, Fredericksburg and Potomac (RF&P) tracks. The station itself would be just south of Springfield Mall beside the proposed Springfield Bypass, which is still under study by state highway officials.

Initial access to the station would be via Frontier Drive, which runs along the eastern edge of Springfield Mall. The station will be built so that no streets in nearby residential neighborhoods, such as Springfield Forest, connect directly with it in order to prevent motorists from using them as short cuts.

Because Frontier Drive will be the only access to the station until -- and if -- the Springfield Bypass is completed in 1986, Metro plans to discourage parking at the station by opening only one of two parking lots planned to hold a total of 3,100 cars.

The lot opened initially would be south of the Springfield Bypass. The other would be north of the bypass and separated from the Springfield Forest subdivision by a screened, 100-foot buffer zone, according to the Metro plan.