RIYADH, Saudi Arabia (AP) _ A U.S. Air Force B-52 bomber returning from a mission in Iraq crashed in the Indian Ocean and three of its six-member crew were missing, U.S. military officials said Sunday.

The huge, eight-engine bomber crashed late Saturday en route back to its base on Diego Garcia, a sand atoll 2,000 miles south of the Persian Gulf.

The command said there was ''no evidence that the aircraft went down as a result of hostile fire.'' It said three of the crew had been rescued and search and rescue efforts for the other three were continuing.

The three MIAs bring to 26 the number of Americans missing in action since the Gulf War began on Jan. 17.

Several dozen of the big B-52 bombers, which date back 35 years in service and were widely used in Vietnam two decades ago, were brought to Diego Garcia in August as part of the buildup for the war against Iraq.

The bombers, whch have a 185-foot wingspan, have been used daily to pound targets in occupied Kuwait. Military sources say they have concentrated their devastating attacks on suspected Iraq troop concentrations, especially those of the Republican Guards, considered Iraq's best troops.

In Vietnam, the B-52s flew hundreds of raids and were regarded as one of the best weapons against enemy troop concentrations.

About two dozen of the high-flying bombers were lost in Vietnam, but because of their vulnerability to anti-aircraft missiles they did not venture over North Vietnam until late 1972, when about 16 were shot down in a period of two weeks during raids designed to force Hanoi to the peace table.

The B-52s normally fly in ''cells'' of three planes, dropping their bomb loads in a box-shaped area about one mile long by a half-mile wide, according to officers knowldgeable about the techniques.

In the current war, the planes reportedly have flown at lower altitudes, with bomb loads at about half the 30 tons that each carried in Indochina.

U.S. military officials say the B-52s are raining 750-pound bombs on the Iraqi targets in Kuwait, with what one called ''fantastic effect'' on the Republican Guards' positions, believed in northern Kuwait near the Iraqi border.

Field reports from the desert near the Kuwait-Saudi border say the rumble of B-52 raids can be heard most nights in that region as well.