Procedural snarls in plans for the Dulles Access Highway Extension project have been worked out, federal officials told the Fairfax County Board of Supervisors this week, and the road could be open by mid-1984 if all goes according to plan.

The 3.7-mile highway project, designed by the Federal Aviation Administration to bring highway traffic to the faltering Dulles International Airport, had been held up for the past year as the FAA studied the project's potential environmental impact.

But Frank Conlin, chief of the FAA engineering staff for metropolitan Washington airports, said this week the environmental impact statement has been completed and is expected to receive final approval by the end of the year.

That done, he said, the FAA will begin conducting public hearings on the proposed design of the project, which will connect I-66 with the Beltway. Congress has thus far appropriated only $17 million of the $35 million needed to build the project, which is expected to carry as many as to 42,000 vehicles daily by 1990, but Conlin said no further financial snags are expected.

"We don't think it's very likely that we'll end up with half a highway and no more money," he said.

Conlin set mid-1981 as the time for beginning highway construction; the work is expected to be completed three years later.

The four-lane highway is expected to significantly improve traffic conditions on surface streets in northeast Fairfax County by reducing use of the already congested streets surrounding Tysons Corner.

The Dulles exention is not seen as a major commuter route, however. During rush hours, only carpools, buses, emergency vehicles and traffic to and from the airport will be permitted to use the road. v

In the off-peak direction and at times other than rush hour, the extension road would be open to all traffic except trucks.

According to an FAA report submitted to the board by Conlin, federal environmental studies found that the project created a potential for pollution in two adjacent watersheds, destruction or disturbance of more than 150 acres of open land and noise pollution at adjacent homes, parks and a school.

FAA plans now call for erosion- control measures, limitations on clearing open land and requirements that landscaping and noise barriers be used to limit the road's intrusion on its surroundings.

Federal officials also are planning to "insure aesthetic quality in design" by seeking recommendations from the Virginia Commission of the Arts and Humanities and the National Endowment for the Arts.

At the same meeting this week, the Fairfax supervisors deflected a bid by unionized firefighters to exchange their eight-hour work days for a schedule that would have professional fire crews work 24-hour days.

Supervisor Sandra L. Duckworth (D-Mount Vernon) had recommended the switch at te urging of the Fairfax County Professional Firefighters Association, which maintains that such a 24-hour schedule would improve firefighter morale and reduce fatigue and sick time.

Currently, Fairfax firefighters work a 56-hour work week of eight, eight-hour days followed by four days off.

The board reacted angrily, however, to what it saw as a union attempt to bypass as established board subcommittee, and decided instead to await a pending subcommittee report on the subject.

In other action, the supervisors enacted permanent legislation to limit the number of new topless bars allowed to open in the county. The board voted to change zoning laws to restrict the location of such establishments to regional shopping centers, such as Tysons Corner or Fair Oaks Mall, despite opposition from mall owners.

The new ordinance makes permanent an "emergency" measure passed in November. Similar legislation has been proposed for the location of "head shops," which sell drug paraphernalia.