The Federal Aviation Administration has formally proposed allowing commuter vehicles carrying as few as two people to use the Dulles Access Road during rush hours. Current rules require at least four people in each commuter car.

The new rules, which would go into effect in September, would stay in force until the scheduled October 1984 opening of the toll lanes that are being built parallel to the access road.

Cars with two or three people would be required to obtain special stickers and enter the access highway at Reston Avenue or Trap Road. They would not be allowed to use Interstate-66 and would have to leave the access highway at the Capital Beltway or at Rte. 123.

The new rules would coincide with a crackdown on "backtracking," a practice in which commuters heading downtown drive first to the airport, loop around and drive toward the city. This allows them to bypass four-person rules in force on the inbound ramps. About 8,000 people back-track each day, the FAA estimates.

The FAA is accepting written comment from the public until July 22. Comments must be sent in duplicate to the Rules Docket (AGC-204), Docket No. 23655, (Notice No. 83-5), 800 Independence Ave. SW, Washington D.C. 2059l, or delivered by hand to Rm. 915G at that address.