Virginia's new transportation secretary, John G. Milliken, has signaled for the first time the state's willingness to use Dulles Toll Road profits for express mass transit service between the international airport and the Tysons Corner area.

That development, plus the availability of a federal grant and a new willingness by the Metropolitan Washington Airports Authority to accept express bus service ahead of rail for Dulles, are breathing life into plans for improved public transit in the traffic-beleaguered 15-mile corridor, officials say.

Although no agreement has been reached, a small "working group" of local, state and regional officials has reached consensus that a start-up system would include frequent bus service between several Dulles corridor parking lots and the West Falls Church Metro station inside the Capital Beltway. The system could be in operation in a few years.

"I think it's a deal that can come together," said James A. Wilding, general manager of the airports authority, a regional body that has strongly advocated rail transit service to the airport. The authority also controls the right of way for the Dulles Access Road and the parallel toll road; the access road median has been reserved for rail service.

In May, Milliken suggested that at least 15 percent of the toll road's profits could be used to finance mass transit if the policy-making Commonwealth Transportation Board concurs.

That represented a significant shift, because earlier this year, before Milliken took office, the state Department of Transportation under Commissioner Ray D. Pethtel had said that all toll road profits -- currently estimated at $10 million a year -- would be needed for improvements to the highway and its interchanges for many years.

Milliken, a former Arlington County Board member and a former Metro Board chairman who was appointed transportation secretary by Gov. L. Douglas Wilder, is also the chairman of the Commonwealth Transportation Board.

Airports authority officials have also shifted their position, saying they would accept bus service as a prelude to a rail system -- rather than insisting on trains first. A bus system can be started much more quickly than rail and, by some estimates, would cost $478 million less.

The authority, in an attempt to persuade the state Transportation Department to free toll road profits for transit, has been threatening to block a planned extension of the toll road between the airport and Leesburg, 15 miles to the west. That issue is still on the table.

The bus system now envisioned would include several large lots where commuters could park their cars, then ride buses to the West Falls Church Metro station near Tysons. The buses likely would run every few minutes during rush hours.

Fairfax County officials last week said that parking lots could be sited in Herndon, Reston and somewhere between Reston and Tysons. An eastern Loudoun County lot is also a possibility.

The buses would likely use the Dulles Access Road, which currently carries airport traffic and nearly 80 daily Metrobus trips. An existing park-and-ride lot similar to the ones envisioned in the plan is operating at capacity in Reston.

The new parking lots could be converted to rail stations if the considerable amount of money needed to construct a rail system and subsidize fares is found, officials said. Estimates of the cost of establishing above-ground rail service in the Dulles corridor, including highway ramps and other amenities, have run as high as $550 million.

Dartrail, a for-profit venture, has been trying to establish rail service between Tysons and Dulles. Company spokesmen said last week that they hope to establish a special tax district in the Dulles corridor through which landowners would help finance a rail system. A similar device has been used to partially finance expansion of Route 28 in Fairfax and Loudoun counties.

Dartrail says it also would like to use toll road profits for a rail system. Milliken recently asked Dartrail to submit ideas for using the money. In the opinion of several transportation specialists, a rail system would have to connect smoothly with Metro to be successful.

A federally funded study last year said bus service and use of car pool lanes would be more cost-effective than new rail service between Tysons and Dulles.

A bus system could cost as little as $72 million and handle 68,000 daily riders by 2010, about 90 percent of what rail service alone could handle.

Rep. Frank R. Wolf (R-Va.) met recently with officials of the federal Urban Mass Transportation Administration and subsequently urged Fairfax officials to apply by December for an UMTA grant under which the federal government and the county would each contribute $36 million to start the bus service.

Fairfax County Board Chairman Audrey Moore said the board favors such a system if the local share can be found. She suggested the county's portion might be raised through a bond referendum this fall. However, Moore said she is concerned that too many federal strings might be attached to an UMTA grant.

Milliken suggested recently that the state could allocate 15 percent of the profits from the current toll road -- close to $2 million annually -- for mass transit, with the figure escalating eventually. The airports authority wants $2 million a year through fiscal 1995 and $12 million annually after that.

The toll road is being widened from two lanes to three in each direction.