Ruined aircraft and the charred bodies of eight servicemen smoldered in a remote Persian desert yesterday, sad symbols of a new American humiliation in Iran.

A bold operation to rescue the 53 hostages in Tehran had ended in disaster 12 hours after it was launched with the highest hopes of success. The survivors of the clandestine American military force escaped from the desert at dawn, leaving dead comrades and equipment behind. They had been defeated, not by the Iranians, but by the mechanical failure of their own aircraft.

As for the hostages, they were reported unharmed in the aftermath of the abortive rescue mission. But their ultimate fate was more unclear last night than at any time since they were taken prisoner on Nov. 4, 1979.

Ayatollah Ruhollah khomeini threatened yesterday to kill them if the United States tries another "silly maneuver." President Carter, he said, has "lost his mind."

Carter, for his part, took responsibility for the mission and its cancellation, expressed disappointment and regret at the deaths of eight men and "a determination to preserve and to bring all of our hostages home to freedom."

"We have been disappointed before. We will not give up in our efforts," the president declared.

Because of weather conditions in Iran and other physical factors, senior administration officials believe that it will be at least six months before the United States could again launch a similar rescue mission, according to The Associated Press.

The debacle left the American government chastened and its allies angry and disheartened. The Soviet Union broadcast a lecture to Carter, charging that "the present master of the White House could not care less about his fellow citizens and is prepared to sacrifice their lives for his election interests."

The Iranians were jubilant. Crowds massed in the streets arms aloft, fists clenched or making the "V" sign for victory. Automobile horns blared in celebration. Around the American Embassy where the hostages are still held, thousands of people chanted new slogans: "Carter Finished," "Down With Carter."

President Carter took full responsibility for the operation. He spoke to the country at 7 a.m., using television. It had been the most difficult 24 hours of his presidency, beginning near dawn in Washington on Thursday when six C130 American transport planes lifted off from a base in southern Egypt for their ultimate destination, a remote airstrip in the Dasht-e-Kavir desert, about 300 miles southeast of Tehran.

The C130s, loaded with fuel, chemicals and other equipment, roared into the twilight on a southerly course. A few hours later, eight helicopters from the aircraft carrier Nimitz headed due north out of the Arabian Sea for their desert rendezvous with the big transports.

They faced a difficult 500-mile flight, approximately the optimum range for the RH53 choppers. They carried aboard 90 men from an elite antiterrorist unit based at Fort Bragg, N.C., a unit sometimes called "Charlie's Angels" as a tribute to its commander, Col. Charles A. Beckwith.

The thwarted operational plan was this:

At the rendezvous point in the desert near the town of Tabas, the helicopters would refuel with kerosene hauled in by the C130s. Then the choppers, each capable of carrying 55 passengers plus crew members, would fly off in the night to a second designated base near the outskirts of Tehran.

There they would hide until the following night -- Friday in Washington -- when the 90 troopers would leave the helicopters, get into prepositioned vehicles and race through darkened streets for the hostage rescue. They would use incapitating gas if needed.

The Americans would all be picked up -- troopers and hostages alike -- by the helicopters, in or near the embassy compound. Their next stop would be a third preselected base east of Tehran where the C130s were to be waiting, engines running, to fly them to safety. The helicopters would be left behind.

But things went wrong from the start. The eight helicopters entered Iranian air space at about 8 p.m., Iranian time, about 10:30 a.m. Thursday in Washington. Within 90 minutes, one of the choppers developed mechanical trouble and made an emergency landing far short of its destination. Its crew and passengers were rescued by another helicopter.

Soon thereafter, a second mishap occurred. A helicopter became lost for two hours in a sandstorm and was forced to return to the aircraft carrier Nimitz.

That left only six helicopters -- the minimum deemed necessary for a successful mission. They all reached the desert rendezvous. The six C130s were waiting there in the darkness.

The refueling was accomplished and the second state of the operation -- the helicopter flight to Base Two near Tehran -- was ordered to begin.

But again, misfortune. One of the helicopters broke down, its hydraulic system malfunctioning.

This changed everything. The whole rescue plan centered on the availability of six choppers. The reason eight had been sent was to assure that the mission would not be jeopardized by a mechanical helicopter failure.

With only five available, the feasibility of the mission was now in doubt. There were discussions on the ground and finally the mission commander sent a message halfway around the world to the Pentagon. He recommended that the mission be scrubbed. An approval came back quickly -- from President Carter in the White House.

The rest should have been simple. The planes, fully fueled, would retrace their course, the helicopters going back to the Nimitz, the C130s going back to their own bases.

But, on this ill-starred night, trouble followed trouble.

Out of the darkness, chugging and lurching, came an Iranian bus, loaded with 50 passengers.

The American troopers had no choice. They stopped the bus and took the Iranians into custody. There was no shooting and no bloodshed, from all accounts. But it was a problem. The Iranians were ordered by Farsi-speaking troopers to stay in the desert until the Americans had left.

Then a truck, followed by a sedan, appeared on the road. The truck was forcibly stopped by the Americans, who fired at it, but the truck driver jumped into the auto behind him, which drove off across the salt flats and escaped.

The planes began their departure and, now, disaster. One of the helicopters, lifting off in the pitch black of the desert night, careered into a C130. There was an explosion. Flames shot up into the sky. Eight Americans were consumed by the fire; four others were burned.

The survivors boarded the five remaining C130s, which trundled down the runway, lifting off just as dawn broke. Below, on the desert floor, the wrecked aircraft burned, funeral pyres for the comrades left behind.

All through this night of disasters, Carter was kept informed. It was noon in Washington Thursday when he learned that the first chopper was down in the desert. Less than two hours later, he knew that two other choppers were in trouble. Shortly before 5 p.m., he ordered the mission aborted. At 6 p.m., he learned of the final disaster.

Seven hours then passed before the terse and shocking announcement by the White House of the failed mission. The delay, it was later explained, was to allow the C130s time to reach safety and to allow Carter and his aides to notify other governments of what had happened. The Soviets were among those informed. They were given assurances that no military attack on Iran was under way and that the mission had been purely "humanitarian," designed only to bring out the American hostages.

Carter returned to this theme in his morning television address.

"The mission . . . was a humanitarian mission," he declared in a flat and weary tone. "It was not directed at Iran. It was not directed against the people of Iran. It was not undertaken with any feeling of hostility toward Iran or its people. It has caused no Iranian casualties."

This language, some in Washington believed, was an implicit appeal to the Iranians to forgo retaliation against the hostages.

It was also a form of reassurance to the Soviet Union, whose forces are poised on the Iranian border and whose leaders have warned the Americans against military action in the Persian Gulf.

The Soviet news agency Tass returned to this general theme yesterday, calling the U.S. mission a form of madness that could bring war to the gulf, "mass bloodshed and the deaths of the hostages."

The government radio in Tehran implied divine intervention for the Iranian cause:

"The world-devouring America, proud of her satanical equipment, had tried to play with fire and had sent forces to the desert. However, the guardian and keeper of this uprisen nation, who from the beginning of this revolution has taken this revolution under the wing of his protection, has inflicted a defeat and flight upon the Americans and their mercenaries unprecedented in their history and the history of the world."

Carter's presidential rivals were charitable. Republican George Bush supported the president's actions without reservation. Ronald Reagan and Edward Kennedy offered sympathy to the families of the dead troopers and called for national "unity."

John Anderson at first called it a "tragic misjudgment," then questioned the timing rather than the operation itself.

Relatives of the hostages were divided in their reaction. "It's a bumbling error by the president," said a Minnesota man, Zane Hall, whose son is a captive. Mary Needham of Bellvue, Neb., was supportive of the president: "We're sorry it didn't work."

Their desparate feelings were reflected in Congress and in seats of government around the world. Rep. Henry Reuss (D-Wis.) demanded that Carter withdraw as a candidate for reelection. Sen. Frank Church and Sen. Charles Percy were on a television talk show soon after dawn, criticizing the president for lack of consultation with Congress.

Others offered sympathy and generous words. "The plan was well-conceived, well-planned and a well-guarded secret," said Sen. Howard Baker (R-Tenn.). "I'm convinced it was a sound plan worth doing. The only quarrel I have with the president was that he should have done it a long time ago."

Iran's forces were put on military alert although Carter and his defense secretary, Harold Brown, gave reassurances that nothing further was contemplated at this time.Brown said the U.S. Strategic Air Command was never on alert during the operation.

Carter and Brown both referred to the rescue mission as a well-conceived operation that had every prospect of success.

The men involved, said the president, "were all volunteers. They were all highly trained.I met with their leaders before they went on this operation. They knew then what hopes of mine and of all Americans they carried with them.

"To the families of those who died and who were wounded. I want to express the admiration I feel for the courage of their loved ones and the sorrow that I feel personally for their sacrifice."

None of the families of the eight Marine and Air Force volunteers killed in the aborted rescue attempt who were reached for comment blamed Carter.

Charles T. McMillan Jr. of Corryton, Tenn., whose son, Charles T. McMillan II, 28, was among the dead, said: "It is not my place to judge. I don't know all the facts . . . . There are so many things we don't know about."

In Pine Bluff, Ark., George Holmes, a prominent attorney, had been notified that his son, Marine Cpl. George Holmes Jr., 22, was missing in action, "but I don't have any thoughts that he survived."

He was not bitter. "If a country has got any national honor or integrity, it's got to take a calculated risk and attempt a mission like this," he said.

General planning and training for some kind of rescue attempt began last November, immediately after the hostages were taken. Carter gave that order. But no specific plan was drawn up at that time.

The troopers involved, all volunteers drawn from the Army, Navy, Air Force and Marines, were part of the Army's Delta Team of Fort Bragg. Their general mission since at least 1978 has been antiterrorist operations. They had never been put to the test until yesterday.

Their training for the Iranian operation reportedly took place in the Southwest United States where the terrain -- notably salt flats -- is similar to the desert area around Tabas.

The specific operational plan for the hostage rescue was ordered into effect on April 11. This was a time of extreme frustration for the administration.

At the end of March a breakthrough had been anticipated -- and announced -- by Carter. On April 2, he promised the Iranians to refrain from threats or hostile statements. There was wide speculation at that time that a favorable response would come quickly from Iran. Those hopes were destroyed on April 7 when Khomenini declared that nothing had changed and that the hostages would remain with their captors at the embassy.

On that day, Carter broke diplomatic relations with Iran, and imposed economic and political sanctions. He also warned that "further options" were available to him, including military action.

Four days later, he made in secret his decision to attempt the rescue mission. Congress was not informed. Nor were the American allies in Europe, Japan and the Middle East.

But in the days that followed there were carefully worded hints that something might be under way. On April 18 he prohibited American travel to Iran and suggested that news organizations consider bringing their people home from Tehran.

Over the weekend, there was a different signal out of the White House. The Los Angeles Times was given details of a White House staff meeting at which various Carter aides expressed alarm and disagreement with the prospect of any form of military action against Iran. The president's chief of staff, Hamilton Jordan, was quoted as reassuring the staff that a rescue mission "had been studied and just wasn't feasible."

The truth, of course, was that the mission even then had been approved and was in its preliminary action stage. The C130s and their crews were being assembled and sent off to Egypt for the flight to Iran. The helicopters were equipped and supplied aboard the Nimitz. The 90-man strike force from the Delta Team was flown out to the Arabian Sea.

All was in readiness. Sometime after lunch on Thursday it began. The C130s first and then the helicopters climbed into the skies of the gulf, bound, this time, not for triumph but for a tragedy with ramifications known last night to no one.

The damage to the national morale remained to be assessed. The prospects for the hostages' release seemed more bleak than in the past. The relations between the United States and its allies were put under new strains. There could be political fallout, too, which could affect the presidential campaign.

The largest unanswered question was this: What next in the hostage drama?