The U.S. soldiers killed in a plane crash in Newfoundland yesterday were members of an unusual autonomous multinational force that has been responsible for peace-keeping in the most sensitive portion of the Sinai Peninsula since Israel completed its withdrawal in 1982.

The Multinational Force and Observers (MFO) has troops from 11 nations, but the United States supplies by far the largest contingent -- 1,100 of the 2,600 total -- and shares the $90 million annual budget equally with Egypt and Israel.

Its first director general, Leamon R. Hunt, 56, a retired U.S. diplomat, was assassinated in February 1984 as he was driving in Rome, where the force has its headquarters. The Red Brigades, an Italian terrorist organization that frequently has attacked Americans, claimed responsibility for the killing, which U.S. and Italian authorities saw as directed against the United States, not the Sinai peace-keeping force. The slaying has never been solved.

Despite the political difficulties that led to its creation and the sensitivity of its role as a buffer between countries that have fought three major wars in the last four decades, however, the force has managed to keep a low profile and has had no combat casualties.

Originally, a U.N. peace-keeping force had been envisioned for the Sinai when Egypt and Israel reached agreement on a peace treaty in 1979. But strong Arab and Soviet opposition to the Egyptian-Israeli treaty made it clear that the United Nations would not sponsor such a force, so the United States and other western nations agreed to form an autonomous multinational force, which was created under a 1981 protocol to the treaty.

The MFO began its duties on April 25, 1982, replacing the U.S. Sinai Field Mission, a force of unarmed American civilian volunteers that, protected by Wackenhut guards, had installed electronic early warning systems and monitored the initial phases of the Israeli withdrawal.

It is the only military force permitted inside Zone C, one of three geographic zones of the Sinai, under the 1979 treaty that provided for Israel to withdraw its troops from the strategic peninsula, which it had captured from Egypt in the 1967 war, and return sovereignty to Cairo.

Zone C forms a buffer between the Israeli border area and the central and western Sinai, in which Egypt is permitted to have limited numbers and types of troops and armaments.

The multinational force, which wears distinctive orange camouflage uniforms, patrols the zone and the Strait of Tiran, between the Gulf of Aqaba and the Red Sea, while a smaller civilian observer force monitors compliance with the treaty.

The 1,100 U.S. troops in the 2,600-member force include 750 in an infantry battalion based at Sharm el-Sheik, at the southern tip of the peninsula, and 350 logistics personnel based at El Gorah, near the Israeli border in the northern Sinai.

The American units come from several U.S. military bases, and the troops serve six-month tours in the Sinai. Another group of U.S. soldiers is scheduled to complete its tour next week, and new forces from Fort Lewis, Wash., are to be rotated in.

Colombia and Fiji each supply about 500 troops to the force, and eight other countries -- Australia, Britain, Canada, France, Italy, the Netherlands, New Zealand and Uruguay -- contribute smaller units.

Since its establishment, the civilian director general of the force -- nominated by the United States and jointly appointed by Egypt and Israel -- has been an American. Since September 1984, the force has been headed by Peter Constable, 53, a retired career Foreign Service officer who most recently served as ambassador to Zaire. The current military commander is a Norwegian, Lt. Gen. Egil Ingebrigtsen.