A Marine Corps V-22 Osprey tilt-rotor aircraft crashed Saturday night near Tucson, killing all 19 Marines aboard, officials said.

The crash of the controversial new aircraft, which can take off and land like a helicopter but fly forward like a plane, is one of the worst accidents in the history of Marine Corps aviation, an official said.

Three of the four crew members of the aircraft were Marines assigned to an HMX-1, the helicopter squadron based at Quantico that flies the president when he travels by helicopter, a Marine spokeswoman said, but she said they had been sent to the Marine air base in Yuma, Ariz., on a temporary assignment to help with testing of the Osprey. Passengers included 14 Marines from the 3rd Battalion, 5th Marines based at Camp Pendleton, Calif., and one from Marine Corps Air Station-Miramar in San Diego County, according to the Marine Corps.

The plane, the 14th of 15 delivered to the Marines, had taken off late Saturday afternoon from the Marine Corps air base in Yuma, Ariz. It was part of a two-aircraft exercise in which the plane was being tested for use in the evacuation of American civilians from a foreign nation--one of the basic Marine Corps missions. At about dusk Saturday, it was approaching a civilian airstrip in Marana, about 25 miles northwest of Tucson.

Officials said they do not know what caused the crash at Marana Northwest Regional Airport or even at what point in the flight it occurred. "We have conflicting reports about whether something happened to it in the air, or whether it exploded when it hit the ground," said Maj. David A. Lapan, a Marine spokesman.

One Arizona official told the Associated Press that witnesses reported seeing the plane plunge "straight downward."

In a statement released by the White House, President Clinton said, "This terrible loss of life is a reminder of how so many men and women in the nation's military put their lives at risk, each and every day, so that we might be a free people, and the cause of peace can be advanced throughout the world."

A team of investigators, led by a colonel from Marine Corps headquarters at the Pentagon, arrived at the crash site yesterday.

The last air crash that killed large numbers of Marines was a mid-air collision between two helicopters at Camp Lejeune, N.C., on May 11, 1996, in which 16 people died. In 1989, 19 Marines died in the crash of a CH-53 helicopter in South Korea.

On Feb. 3, 1998, 20 European civilians were killed when a Marine jet on a training mission sliced through the cable of a ski lift in northern Italy, killing everyone aboard a ski gondola.

Saturday's crash marks the second time that people have been killed while testing the Osprey, which now has undergone 2,500 hours of evaluation. On July 20, 1992, seven people were killed when an Osprey plunged into the Potomac River near the Marine Corps base at Quantico after a fire began aboard. A third Osprey crashed a year earlier while hovering at a Boeing test facility near Wilmington, Del., but caused no fatalities. A 1999 Pentagon report on the V-22 noted that a mechanical failure aboard another Osprey caused a fire on board the plane that was extinguished by an automatic fire suppression system built into the wing, "thus saving the aircraft from a catastrophic loss."

The latest Osprey accident may raise questions about the future of the program at a time when Congress is skeptical of Pentagon plans to spend hundreds of billions of dollars in coming decades on tactical aircraft--the V-22, the Air Force's F-22 supersonic fighter, the multi-service Joint Strike Fighter and the latest version of the Navy's F-18 fighter and attack jet.

The Osprey is a unique aircraft, the first ever designed to combine the speed and range of an airplane with the takeoff and landing capabilities of a helicopter. It does this by taking off with its two 38-foot-long, three-bladed rotors pointed upward, then tilting them forward 90 degrees for regular flight. To land, it can tilt its rotors back again, permitting it to land like a helicopter. It does this while carrying as many as 24 Marines loaded with their weapons and combat supplies.

Critics have said the plane, which was estimated last month by the Congressional Budget Office to cost about $60 million apiece, far more than conventional helicopters, is too expensive given the relatively small load it carries. Some have advocated instead that the Marines buy UH-60 Black Hawk helicopters, which are used extensively by the Army.

But the Marines maintain that the overall $37.3 billion price tag on the Osprey program will be worth it because it gives them a revolutionary ability to attack with great speed over a far greater area. The service calls the new plane "critical" to its ability to operate in the 21st century. The Marines plan to replace all their current troop-carrying helicopters with the V-22, acquiring about 360 of the new aircraft over the next 10 years. The Navy and Air Force each plan to buy about 50 of the planes, which are jointly built by Bell Helicopter Textron and Boeing Co.

The first squadron of Marine V-22s, of which the crashed plane was to have been a part, is scheduled to begin operations soon at the Marine air station at New River, N.C.

Staff writer Josh White contributed to this report.

Crash Victims

Following are the Marine crew members and passengers killed in the Osprey accident Saturday:

Crew assigned to Marine Helicopter Squadron-1, Quantico:

Maj. John A. Brow, 39, pilot, California, Md.

Maj. Brooks S. Gruber, 34, pilot, Jacksonville, N.C.

Cpl. Kelly S. Keith, 22, aircraft crew chief, Florence, S.C.

Crew assigned to Marine Medium Tilt-Rotor Training Squadron:

Staff Sgt. William B. Nelson, 30, aerial observer/mechanic, Richmond.

Passengers assigned to 3rd Battalion, 5th Marine Regiment, 1st Marine Division, Camp Pendleton, Calif.:

Sgt. Jose Alvarez, 28, machinegunner, Uvalde, Tex.

Pfc. Gabriel C. Clevenger, 21, machinegunner, Picher, Okla.

Pfc. Alfred Corona, 23, machinegunner, San Antonio.

Lance Cpl. Jason T. Duke, 28, machinegunner, Sacramento.

Lance Cpl. Jesus Gonzalez Sanchez, 27, assaultman, San Diego.

Lance Cpl. Seth G. Jones, 18, assaultman, Bend, Ore.

2nd Lt. Clayton J. Kennedy, 24, platoon commander, Clifton Bosque, Tex.

Lance Cpl. Jorge A. Morin, 21, assaultman, McAllen, Tex.

Cpl. Adam C. Neely, 22, rifleman, Winthrop, Wash.

Pfc. Kenneth O. Paddio, 23, rifleman, Houston.

Pfc. George P. Santos, 19, rifleman, Long Beach, Calif.

Pfc. Keoki P. Santos, 24, rifleman, Grand Ronde, Ore.

Cpl. Can Soler, 21, rifleman, Palm City, Fla.

Pvt. Adam L. Tatro, 19, rifleman, Brownwood, Tex.

Passenger assigned to Marine Air Control Group 38, Marine Corps Air Station-Miramar in San Diego County:

Cpl. Eric J. Martinez, 21, field radio operator, Flagstaff, Ariz.

Osprey's Capabilities

An Osprey MV-22 tilt-wing aircraft crashed in Arizona Saturday, killing all 19 people aboard. The aircraft was on a training mission from the Marine Corps Air Station at Yuma.

The MV-22 Osprey can take off and hover like a helicopter. With its rotors tilted forward, it flies like a conventional propeller-driven airplane.

SOURCES: Bell -- Boeing, KRT Graphics