Four U.S. Navy jet fighters intercepted an Egyptian airliner carrying the four Palestinian hijackers of the Italian cruise ship Achille Lauro in international airspace and forced it to land early Friday morning at a U.S. Navy air base in Sicily.

The plane was surrounded immediately by U.S. and Italian troops, and the four hijackers were taken into custody by the Italians for legal proceedings. In Washington, White House officials said they intended to pursue prompt extradition proceedings.

The office of Italian Prime Minister Bettino Craxi said the four U.S. jets, F14s from the aircraft carrier USS Saratoga, and the Egyptian Boeing 737 landed at the U.S. Navy's Sigonella Air Base at 12:30 a.m. (7:30 p.m. EDT) for a "technical stop." An Italian government statement said that Craxi had agreed to a request from President Reagan that the planes be allowed to land there.

U.S. Defense Secretary Caspar W. Weinberger, in a briefing at the Pentagon after midnight Washington time, said the four terrorists were in Italian custody, as well as two other Palestinians also found on the airliner who are being investigated by Italian authorities. The Egyptian crew will be permitted to return the airliner to Cairo "at their convenience," the secretary said.

In providing details of the military operation, Weinberger said that the Saratoga was off the coast of Albania when it received orders at 7 p.m. Rome time (2 p.m. EDT) to prepare for action. All operations throughout the military intercept were carried out in darkness, Weinberger said, and the carrier had to be turned around because it was heading in the wrong direction at the time the order was given.

The Egyptian airliner left Cairo around 4:15 p.m. EDT and was intercepted just south of Crete by the F14s, which were supported by E2C Hawkeye electronic surveillance planes and other support aircraft. The fighters arrived on the airliner's flight path, where they waited for the quarry and electronically picked it out from other air traffic in the region, Weinberger said.

No refueling of the fighters was necessary, he said. The airliner had been refused permission to land in Tunis and Athens but apparently was headed toward Tunis when it was intercepted, Weinberger said.

[Other U.S. military sources said the pilot of the Egyptian plane seemed surprised when he was intercepted and offered no resistance. These sources said the airliner initially was difficult to find.]

The capture of the terrorists climaxed a bizarre series of events beginning with the hijacking last Monday of the Italian cruise liner with more than 400 passengers and crew members on board. Before the hijackers gave up, one American had been killed.

The dramatic development in the air over the Eastern Mediterranean Thursday night occurred after the U.S. government had reacted with anger and irritation at Egyptian government plans to allow the four hijackers to leave Egypt for an undisclosed destination without prosecuting them for the hijacking and murder of Leon Klinghoffer, 69, of New York City.

Italy and the United States had demanded that the four hijackers be made available to be put on trial. Italy has insisted that the four should be tried here because the ship they hijacked was an Italian vessel and thus the slaying of Klinghoffer, had occurred on Italian territory, meaning the ship.

Egyptian President Hosni Mubarak had said Thursday that the four hijackers who had surrendered Wednesday to Egyptian authorities had left Egypt five hours later and were the responsibility of the Palestine Liberation Organization, which had negotiated their surrender. The hijackers had said they were members of a faction of the PLO.

The U.S. government, however, announced late Thursday that the four hijackers were still in Egyptian hands and were at an Egyptian Air Force base outside of Cairo waiting for a plane to take them out of the country. Washington demanded that the Egyptian authorities turn the hijackers over to a sovereign nation for prosecution for the death of Klinghoffer, a retired businessman from Manhattan who was confined to a wheelchair after a stroke.

Reports here originally said that the Egyptian plane had filed a flight plan for Algeria, then changed it in midair and asked for permission to land in the Tunisian capital of Tunis, where the PLO has its headquarters.

When Italy believed the four were in PLO custody Thursday evening, it ordered the Foreign Ministry to enter into negotiations with the PLO to have the four hijackers brought here for trial.

Earlier on Thursday, special correspondent Jeffrey Bartholet reported from Cairo:

President Mubarak and other Egyptian officials had insisted throughout the day that the four hijackers had left Egypt within hours after surrendering on Wednesday. The Egyptians had defended their handling of the affair in the face of criticism from the United States.

Mubarak told reporters Thursday morning that the hijackers had gone and were the responsibility of the PLO, but PLO leader Yasser Arafat said they were "under the Egyptian authorities' control."

"They left the country, I don't know where they went," Mubarak said. Then in answer to a question, he added, "maybe Tunisia," where the PLO has its headquarters.

At a press conference later, Foreign Minister Esmat Abdel-Meguid told reporters, "They left Egypt. I know where they are, but I'm not going to tell you.

The Achille Lauro remained at Port Said, on Egypt's Mediterranean coast, and several of the more than 400 freed hostages, including about a dozen Americans, left the ship to return home. Among them was Marilyn Klinghoffer, whose husband had been killed by the hijackers on Tuesday and, according to accounts from the ship Thursday, was pushed overboard with his wheelchair.

Showing clear sensitivity to the harsh criticism from the United States for their supposed release of hijackers who had killed an American hostage, Mubarak and Abdel-Meguid insisted that at the time the agreement negotiated by the PLO was approved Wednesday, they were unaware of Klinghoffer's death.

Mubarak said that "if the captain had told us that a passenger had been killed, we would have changed our position toward the whole operation. But when this emerged, we already had sent the hijackers out of the country."

Later, Mubarak questioned whether Klinghoffer had actually been killed. "There is no body and no proof he had been murdered," he said, according to Egypt's official Middle East News Agency. "Maybe the man was in hiding or did not board the ship at all."

Abdel-Meguid complained to reporters Thursday night, "I don't like the insinuations in the United States now. This is very unfair. . . . I cannot accept any insinuations and I reject them totally. We believe we have done our duty."

Abdel-Meguid pointed out that in the negotiations for the release of the American hostages in the hijacking of a Trans World Airlines plane last June, the hijackers were allowed to go free, although they had killed an American hostage, and Israel later gave in to their demands to release Shiite Moslem prisoners it was holding.

"Thanks were given to Syria for their help," he said. "Let's be serious. This matter should be put in its proper perspective."

Egyptian officials, however, offered incomplete and seemingly contradictory information throughout Thursday about the release of the hijackers.

Early in the day, Mubarak said the hijackers had left the country within five hours of their surrender, which took place at 4:30 p.m. Wednesday, and said they were "now the responsibility of the PLO."

But all day, the PLO denied having possession of them, fueling speculation and rumors about their whereabouts and about what sort of deal had been made to secure the release of the more than 400 passengers and crew who had been held hostage on board the luxury liner since Monday.

Asked Thursday night at what time the hijackers had left, Abdel-Meguid refused to say. "I'm not keeping a chronometer watch," he answered, and then said later, "They will soon be in the hands of Mr. Arafat."

Adding to confusion was a statement Thursday morning by Abdul Rahman Saramawi, the governor of Port Said, that the pirates "are still in custody, and it remains to be determined whether they will be tried."

Abdel-Meguid said the Egyptians had decided to negotiate with the terrorists reluctantly.

At 10 p.m. Tuesday, he said, when he heard that the liner, which had been barred from landing at Syria, was returning to Egypt, he said he awakened the ambassadors of Italy, France, Britain and West Germany, and asked them what they wanted to do.

They replied that they would get in touch with their capitals, and get back with a decision.

He said that he told the ambassadors, "We are not interested in dealing with this group, and might ask the ship to get out."

Maguid added that the ship never entered Egyptian territorial waters, but remained 16 miles north of Port Said.

The following morning -- Wednesday -- Egyptians began contact with the terrorists, at the request of some western nations, so as not to be caught off guard, Abdel-Meguid said.

At the 1:30 p.m. meeting with the four ambassadors, he said, he asked them to sign a statement that "strongly urged" Egypt to use "our efforts to seek the release of the ship." But only two -- those from Italy and West Germany -- signed it.

Abdel-Meguid said he told the ambassadors that Egypt negotiated only at the urging of concerned nations who had citizens on board. "I said we could make the ship go away -- that would have been the easiest," he said.

At some point Wednesday afternoon, Abdel-Meguid said, six helicopters began flying over the hijacked liner, and the terrorists threatened to blow it up.

He said the Americans denied they were U.S. helicopters so Egypt contacted Israel. He said nothing of the Israeli response.

Abdel-Meguid said Egypt's primary goal was to "save the lives of the passengers." He said that if Egypt had known about the death of Klinghoffer, "We would never, never have pursued the operation."