Two U.S. Air National Guard officers were killed yesterday when their fighter jet crashed in the United Arab Emirates and eight Marines remained missing after two transport helicopters disappeared over the Gulf of Oman during night operations, according to military officials.

An F-4 Phantom fighter jet crashed in the U.A.E. on the southeastern side of the Arabian peninsula at 1:10 p.m. local time yesterday, killing both crew members from the Alabama Air National Guard 117th Tactical Reconnaissance Wing, authorities said. The dead were identified as Maj. Barry K. Henderson, 40, of Tuscumbia, Ala., and Maj. Stephen G. Schramm, 43, of Birmingham.

The Air Force is investigating the cause of the crash, a Pentagon spokesman said.

The two Marine Corps UH-1 Huey transport helicopters based on the amphibious assault ship USS Okinawa in the Gulf of Oman just outside the Persian Gulf disappeared at 5:13 a.m. gulf time yesterday with eight men aboard during "routine night training operations" over the water, officials said.

The ship "lost communication and radar contact" with the two aircraft simultaneously, according to Pentagon spokesman Glenn Flood. "They immediately started search and rescue efforts."

The Pentagon said search crews had spotted the wreckage of at least one helicopter, but had not found the crew.

Prior to yesterday's accidents, 20 U.S. troops had died in incidents related to Operation Desert Shield. Military officials said the number of deaths so far is relatively low given the size of the Middle East operation. About 200,000 troops -- 10 percent of the U.S. armed forces -- are now assigned to the Arabian peninsula and surrounding waterways.

"These things are a tragedy," Defense Secretary Richard B. Cheney said yesterday. "Any loss of life is something we try, to the best of our ability, to avoid."

But Cheney added that given the size of U.S. forces operating in the region and the complexity of their weapons and equipment, "there are, from time to time, accidents."

Fifteen people have been killed in air accidents in connection with the Middle East operation, including 13 who died when an Air Force C-5A transport bound for Saudi Arabia crashed in Germany Aug. 28. Two Air Force officers died when their F-15 fighter jet crashed Sept. 30.

Three men have died as a result of automobile accidents, a sailor was electrocuted doing maintenance work aboard a naval ship and a Marine died of a self-inflicted gunshot wound.

Although military officials have not disclosed details of airplane and helicopter crashes in the Middle East, some pilots have complained about the supervision of air traffic in the congested area. Most airfields in Saudi Arabia, the U.A.E., Oman and Qatar have been filled to capacity, with aircraft from half a dozen nations attempting to coordinate their operations.

Pentagon officials said a dozen helicopters have crashed or been damaged in accidents in the Saudi region since the influx of U.S. forces.