WASHINGTON (AP) — The commandant of the Marine Corps grounded all MV-22 Osprey aircraft Tuesday following a crash in North Carolina that killed four Marines and raised new doubts about the future of the tilt-rotor plane.

Gen. James L. Jones, the commandant, also asked Defense Secretary William Cohen to convene a panel of experts to review the troubled $40 billion program, said Marine Corps spokesman Maj. Dave Andersen at the Pentagon.

"This program is very, very important to the Marine Corps, to me and I think to the nation, and we're going to work very hard to find out what happened," said Lt. Gen. Fred McCorkle, head of Marine aviation.

An Osprey crashed Monday night in a forested area near Jacksonville, N.C., killing all four Marines aboard. It was the second fatal Osprey accident this year. In April an Osprey crashed while attempting to land at an airport in Arizona, killing all 19 Marines aboard. Human error was blamed for that accident.

At Marine Corps headquarters, Andersen said Jones has asked the Pentagon to delay indefinitely a decision that was due this month on giving the go-ahead to begin full-rate production of the Osprey, which is a revolutionary tilt-rotor aircraft that takes off and lands like a helicopter and flies like an airplane.

Jones wants the decision put off "until further information is gathered" regarding the Jacksonville crash, Andersen said.

The four killed in Monday night's crash were identified by Marine Corps headquarters as: Lt. Col. Keith M. Sweaney, 42, of Richmond, Va.; Maj. Michael L. Murphy, 38, of Blauvelt, N.Y.; Staff Sgt. Avely W. Runnels, 25, of Morven, Ga.; and Sgt. Jason A. Buyck, 24, of Sodus, N.Y.

The Jacksonville crash is under investigation. The last communication with the aircraft, based at the Marine Corps Air Station at New River, N.C., was a mayday call received at 7:27 p.m., officials said.

"The pilot gave no specifics on the nature of the situation, just that it was a mayday," McCorkle said.

"The rotors got real loud, and it disappeared behind a tree," said Mark Calnan, who lives near the crash site in a southeastern North Carolina forest. "There was an orange flash, a great big one. Then I heard a pop. It crackled like thunder."

Rescue workers had to use a bulldozer to reach the site about 10 miles north of Jacksonville.

The Osprey program has had a troubled history. There were nine aircraft in the Marines' inventory before the Monday crash. A prototype version crashed in June 1991 while undergoing its first flight in Delaware, and in July 1992 another prototype Osprey crashed near Quantico, Va., killing seven people.

Just last month, Jones, the Marine commandant, said he fully expected the Pentagon to give the go-ahead to begin full-scale production of the Osprey, which is built jointly by Boeing Co. and Bell Helicopter Textron.