Springfield residents are unanimous in their support for a future subway station in the Franconia area, but are concerned that the station could contribute to backed-up traffic at the I-95 interchange, overloaded roads at Springfield Mall and increased parking and noise problems.

Area residents testified last week at a hearing on final plans for the station, scheduled to open in 1986.

The Franconia-Springfield station already has spurred about $60 million in area development, but is threatened by a cutback in federal funds recently announced by the Reagan administration.

Residents also are concerned that the station will open before the completion of at least part of the controversial $200 million Springfield Bypass. Without the bypass, or a spur of the bypass, area residents say the subway station will be isolated in a cul-de-sac on a small road behind Springfield Mall.

The bypass is unlikely to be completed before 1987, county and state officials said last week, even if it is approved and funded. That means the Metro station could be open for nearly a year before the bypass is completed.

Fairfax County and the state have listed the bypass as a high-priority project, although the Board of Supervisors has been divided on the issue, particularly on the route the road would take across the county.

However, there appears to be almost countywide agreement on the need for the Metro station and for at least the section of the bypass to serve the station.

Supervisor Marie B. Travesky called the Metro section of the bypass crucial because "most people will be coming to Metro from the west and there will be no way to get them here."

The latest plans for the Springfield Bypass will be released at the end of the month in an environmental impact study of three major routes proposed for the 30-mile highway. The four-to-six lane road will swing like an outer Beltway from Rte. 7 in Reston to Rte. 1 at Fort Belvoir.

A public hearing on the bypass is expected to be held before June, with a final route recommended this summer and a decision by the state Highway Commission expected as early as this fall.

However, some residents at the hearing were not optimistic about the chances of the bypass being built in time for the opening of the Metro station.

"The Springfield Bypass is controversial, may not be built at all and I doubt that it will be constructed in this decade because of money problems," testified Thomas J. C. Williams of the Leewood Forest Homeowners Association. "And if it isn't built to Metro, traffic will be backed up at the Springfierld interchange even worse than it is now and overload roads around Springfield Mall which already are overloaded."

Williams accused Metro of seriously underestimating the potential ridership, and thus the traffic, at the Franconia-Springfield station, Metro estimates "peak rush-hour ridership of 3,560 passengers by 1990. . . I predict we will be at that maximum within one year" of the station's opening, Williams said.

David Amick, representing Springfield Forest, a subdivision of more than 200 homes north of the station site and adjacent to one of two large parking lots for the station, said a major concern is that an adequate buffer zone be built to act as a noise and visual barrier between the station and residential areas. He said residents also want to be sure measures will be taken to prevent commuters from using residential streets for all-day parking.