Federal investigators planned yesterday to check the quality and amount of fuel carried by the commuter airplane that made a forced landing onto a grassy field south of Dulles International Airport Thursday night.

"We have not ruled out the possibility of fuel starvation, but there were no early signs of it," said Michael Benson, a spokesman for the National Transportation Safety Board.

The board, which is investigating the accident, plans laboratory tests on a fuel sample and an examination of fuel records as part of its inquiry, Benson said.

Investigators also praised the pilot of American Eagle Flight 3464 for landing the 19-seat turboprop upright and generally intact, with one serious injury.

The pilot, copilot and five of the six passengers were treated for minor injuries, a spokesman for Fair Oaks Hospital said.

However, Richard Schmidt, 50, of Pittston, N.J., a pilot for the airline who was a passenger on this flight, was hospitalized in fair condition yesterday, the spokeswoman said. She would not comment on news reports that Schmidt had broken a vertebra.

The pilot in command, Michael Farb, of Raleigh, N.C., told investigators that the 19-seat, twin-engine Swearingen Metro II turboprop lost power in the left engine as the aircraft was approaching the runway with the flaps on the rear of its wings extended and the landing gear lowered.

"The captain said he was having a power problem and realized he was not able to make the runway," said Barry Trotter, the safety board investigator in charge.

Farb "did a spectacular job" of landing the plane on the hilly site, just off Rte. 28 and Westfield Boulevard, Trotter said. "It was relatively smooth," Trotter said. The aircraft had a broken left landing gear and bent nose as a result of the landing.

Farb told investigators that "he knew the area and was familiar with the terrain" around Dulles, Benson said. "It paid off."

Some passengers and witnesses said they believed both engines were out.

Aviation experts said yesterday that engine failure is frequently caused by fuel problems, which can include running out of fuel, contamination, a leak or another interruption in the fuel supply system. There was no fire, which is sometimes an indication of a lack of fuel.

The aircraft "took on fuel" in Newark before leaving for Dulles, said Larry Rednour, a spokesman for AVAir Inc., a Raleigh-based company that operates the aircraft. AVAir flies its 28 airplanes under the name American Eagle as part of a marketing agreement it has with American Airlines.

The safety board team also planned to remove, dismantle and closely examine the engines, manufactured by Garrett Corp. of Los Angeles, and other parts of the airplane, according to Trotter.

Investigators also plan to examine maintenance records and listen to the Dulles control tower tape of the pilot's communications, Trotter said. The aircraft was not equipped with a flight data recorder or cockpit voice recorder, the so-called black boxes that are required in full-size commercial jets.

Farb joined the airline in April and had flown about 600 hours since then, said AVAir's Rednour. The airline was unable to provide information of Farb's previous experience.

AVAir is a regional carrier primarily flying passengers to American Airlines' Raleigh-Durham hub, Rednour said. The privately held company started operations in May 1985 when it purchased the assets of Air Virginia, which was based in Lynchburg, he said.