The Dulles Airport Access Road, a 13-mile-long expressway that is effectively closed to thousands of Northern Virginia commuters, should be opened to car pools, Transporation Secretary Brock Adams has decided.

Adams' decision technically is subject to approval by other agencies and will require the cooperation of both Fairfax County and the Virginia highway department, but his approval is crucial because the highway is owned by the Department of Transportation.

Private automobiles not traveling all the way to or from the airport have been prohibited from using the road except or special occasions since it was opened in 1962. The four-lane road was constructed that way to guarantee that only airline passengers would be able to get to and from Dulles without difficulty.

Adams said he was concerned about prrotecting the Dulles traffic and thus protecting the Dulles traffic and thus imposed several conditions in opening the highway to commuters:

Four-person car pools will be permitted on the access road only until Jan. 1, 1985. At that time, it is presumed National Airport's annual passenger total will have reached a ceiling of 18 million and that Washington's air traffic growth will be occurring at Dulles. It is also presumed that Interstate Route 66 will be completed from the Capital Beltway to Washington and that a parallel toll road to the Dulles Access Road will have been opened.

Virginia must agree with the Department of Transporation on an enforcement plan to guarantee that cars entering the acess road at the Reston ramps contain at least four people.

Adams also said that when the access road is extended from the Beltway to Interstate 66 that the extenson will be restricted during rush hours to car pools, as will be i-66 inside the Beltway.

Adams said in an interview yesterday he had planned to release his Dulles Access Road Study at the same time he released his expected new policy for National Airport.

However, the National Airport Policy is snagged on several points and, Adams said, "I just feel that now, in terms of the energy situation, we ought to go with car pools."

Rep. Joseph L. Fisher [D-Va.], a longtime advocate of opening the Dulles road to car pools, agreed. "There are a few conditions." he said yesterday, "but I think we can live with them." Fisher said that it "shouldn't be too long" before the existing ramps are opened to car pools.

About 3,500 automobiles a day already use the Dulles Access Road for commuting. They enter at various onramps, drive west to the airport, turn aound, heading east to the Beltway. Adams' report estimates that 540 car pools will be using the Dulles road by 1984, but he said yesterday that figure was probably too low in light of the energy situation.

If the current car pool use of express lanes on Shirley Highway [Interstate 395] is any example, Adams' figure is vastly understimated. The Shirley express lanes were opened to car pools a few years ago and now carry about 3,500 car pools, or a minimum of 14,000 people, per day.

Adams recommendation of carpooling came in a report to Congress required by the Surface Transportation Act of 1978. Fisher was responsible for getting that requirement into the act and has made frequent inquiries into the report's progress.

The Dulles Access Road lies entirely in Fisher's Northern Virginia district. It parallels Virginia Route 7, which has been badly overburdened by traffic generated in the bustling Tysons Corner-Herndon corridor. Rush hour commuting on Route 7, with its many traffic signals, has become increasingly difficult and has added pressure on officials to open the Dulles road.

Before the car pools can be added, an environmental assessment must be completed and the recommendation must be reviewed by the National Capital Planning Commission. The report to Congress said that a long, formal environmental impact statement should not be required.

The access road has been used by commuter buses from Reston since 1973, and has been opened to two-way traffic for events at Wolf Trap Farm Park, near Vienna. CAPTION: Map, The Dulles Airport Access Road may soon be opened to car pools of commuters. By Dave Cook -- The Washington Post