The Fairfax County Board of Supervisors voted unanimously last night to ask the Virginia Department of Highways and Transportation to build a toll road parallel to the Dulles Airport Access Road.

The State Highway Department which already has the authority to build the toll road is awaiting the results of a study that will say whether there is enough traffic in the area to pay off the cost of building the road.

It would be the first toll road the state has built in the Washington suburbs.

The study will also indicate what the construction costs of the toll road should be and how much the tolls on it should be, Hirst said. The state currently charges tolls of 25 cents a car for use of a toll road of similar length that it operates in Virginia Beach.

Construction of the parallel road has long been advocated by the Fairfax supervisors, and would speed commuter travel between Washington and the Herndon-Reston area. It would also open up the airport road corridor to industrial development, count officials say.

Use of the Dulles Access Road, which runs just east of Tysons Corner to the airport at the Loudoun County line, is limited primarily to airport traffic - a point that has long angered commuters who live along the road.

State Sen. Omer L. Hirst (D-Fairfax), who introduced legislation empowering the state to construct the toll road, said yesterday the board's action will encourage the state "to move a little faster" in construction of the load.

Hirst, acting chairman of the Senate Transportation Committee, said it is his "instinctive feeling" that the study of the toll road will show there is a sufficient volume of traffic to justify building it.

"We are just waiting for the report," Hirst said. The report is due Oct. 1.

Development of the Dulles Access Road corridor "is one of the most valuab assets Fairfax County can look for in its efforts to increase economic development activity, broaden its tax base, and provide much needed tax relief to the homeowner," according to a report presented last night by the county's Office of Comprehensive Planning.

The report said land within the corridor represents nearly 31 percent of all land planned for industry or commercial offices in Fairfax.

In a comparison of Fairfax to its equally affluent neighbor in Maryland, Montgomery County, the report said the Dulles Access Road corridor contains nearly twice the amount of land planned for industry as that along Montgomery County's Interstate Rte. 270 corridor.

Virginia highway authorities historically have been amenable to building toll roads in urban areas. Toll roads have been constructed by the state, at the request of local governments, in the Richmond and Norfolk areas.

Shiva Pant, director of the county's Office of Transportation, said last night that construction of the parallel lanes will "in no way" affect other allocatons of state money for highway construction in Northern Virginia.

The Federal Aviation Administration, which owns the right-of-way along the Dulles access road, has repeatedly indicated its willingness to provide land for construction of the parallel lanes if the state were willing to pay for construction.

Hirst said last night the advantage of issuing state revenue bonds is that construction money for the road can be raised quickly. Under normal annual highway allocation, Hirst said, it might take years before sufficient funds were available to complete the road.

The report presented yesterday by the county said construction of the parallel lanes may in fact reduce traffic heading into Washington by increasing the number of jobs inside Fairfax County.

The increased number of industrial jobs and changing traffic patterns, the report said, would "relieve eastbound and westbound traffic in the morning and evening rush hours."