In a move that seems certain to fail, the Fairfax County Board of Supervisors voted 5 to 4 yesterday to ask the Federal Aviation Administration to open up the Dulles access road to commuters until a planned parallel toll road is built.

After hearing about the board's request, Jim Murphy, an FAA official in charge of running Dulles International and National airports, said, "Our position has been no. The Dulles access road was built to provide the speediest possible access to Dulles Airport."

Murphy said he doubts that the FAA position will change. Commuters in the Reston and Herndon area have for years pushed for access to the four-lane highway, which is owned and operated by the FAA.

Supervisor Martha V. Pennino (D-Centreville), who introduced the board's motion, said yesterday that FAA officials always have kept commuters off the highway "because they feared commuters would be on there and they would never get them off."

Commuter use of the highway, however, would not be permanent, pennino said, because the parallel toll road is expected to be completed by 1982 or 1983.

The present limited access highway speeds traffic without interruption from the Capitol Beltway to Dulles International Airport. Ramps have been constructed for the exclusive use of commuter buses from Reston, and the Wolf Trap Farm exit is opened to traffic when performances are held there.

In addition to Pennino, voting in favor of asking the FAA to open the road were supervisors Warren I. Cikins (D-Mt. Vernon), Joseph Alexander (D-Lee), John P. Shacochis (R-Dranesville) and Republican board chairman John F. Herrity. Voting against the motion were Marie Travesky (R-Spingfield), Audrey Moore (D-Annandale), Alan Magazine (D-MAson) and James Scott (D-Providence).