The Palestinian hijackers of an Italian cruise ship abandoned the vessel and ended the two-day-old drama on the high seas today, in return for an Egyptian pledge of safe conduct out of the country. But the captain of the pirated vessel disclosed that one of the more than 500 hostages aboard, a disabled, 69-year-old American, had been killed by the hijackers and thrown overboard yesterday.

The ship, the Achille Lauro, was reported tonight to be preparing to resume its cruise. The next stop was supposed to be Ashdod, Israeli. There were strong indications that Ashdod was the original target of the hijackers, who had hoped to enter Israel as tourists for an unspecified terrorist attack. Israeli officials and other sources suggested that something went awry with the original plan, causing the Palestinians to hijack the ship instead.

Late tonight some doubts were raised as to whether the ship had left for Ashdod or was still near Egypt.

The four hijackers left the ship after negotiating with Palestine Liberation Organization representatives today off Port Said, an Egyptian port on the Mediterranean, and Egyptian Foreign Minister Esmat Abdel-Meguid said that they "are heading out of Egypt."

There was no indication where they would be sent, but PLO leader Yasser Arafat, who denied his group was involved in the piracy, asked that they be turned over to him so that the PLO could "punish them."

An Egyptian official in Washington said privately that the hijackers were allowed to leave by boat without coming ashore in Egypt. This arrangement, he said, was based on early reports that no hostages had been harmed.

But when U.S. Ambassador to Egypt Nicholas Veliotes visited the ship off Port Said tonight to check details of the situation and discovered that Leon Klinghoffer had been murdered, he demanded by radio phone that the Egyptians prosecute "those sons of bitches."

White House spokesman Larry Speakes said the United States was "saddened and outraged by the brutal killing of an innocent American" and urged Egypt "in strong terms" not to let the four pirates responsible for the killing leave Egypt as Cairo had initially agreed to.

Italian Prime Minister Bettino Craxi, who at a news conference in Rome was the first to report the death of Klinghoffer, praised Arafat for his negotiating role and said that Italy had been prepared to use military action tonight to end the crisis if the standoff had continued, Washington Post correspondent Loren Jenkins reported from Rome.

The circumstances of the killing of Klinghoffer, who relatives said was confined to a wheelchair as a result of a stroke five years ago, were unclear. An officer of the ship told ABC that one of the hijackers, with blood on his trousers, "said he had killed him and thrown him overboard."

Klinghoffer apparently was killed, the ship's captain, Gerardo de Rosa, told CBS by ship-to-shore radio, because the hijackers could not get authorities to negotiate with them. They threatened to kill more, de Rosa said, speaking in broken English, "but they kill just Mr. Klinghoffer."

De Rosa told CBS that the hijackers had threatened to kill all the Americans on board, "then the English, then the others." After killing Klinghoffer, De Rosa said, "they say the second one will be Miss Mildred," an apparent reference to Mildred Hodes, of West Orange, N.J., but there was no indication that she, or Klinghoffer's wife, Marilyn, who was also aboard, were harmed.

Another hostage on the ship, Seymour Meskin, of Union, N.J., told CBS that one of the terrorists "seemed to really have it in for the Americans," and kept "browbeating" and "threatening" them.

"There were one or two instances of somebody being hit -- not badly, but minor things," Meskin said.

The 44-hour drama, the first hijacking of a major cruise vessel in nearly a quarter of a century, ended at about 5 p.m. local time when the four terrorists who seized the luxury liner Monday were persuaded to leave the ship.

The surrender came after a day of tense negotiations. The key intermediary reportedly was Mohammed Abbas, also known as Abu Khaled, who is a member of the PLO Executive Council and was dispatched to Egypt by Arafat.

Also involved in the negotiations was Hani Hassan, a senior political adviser to Arafat who was in Egypt on an official visit when the hijacking occurred, and Zahdi Qoudra, the PLO representative in Cairo.

Together with Egyptian authorities, the PLO officials reportedly persuaded the terrorists to give themselves up after extended discussions over ship-to-shore radio. Some of these were monitored by reporters ashore, but the terms of the surrender were not immediately clear. At least one message was carried from the ship to port by a fishing boat.

The arrangement for the release was completed, according to radio messages, when Abbas and Egyptian authorities went to meet with the hijackers on the liner.

In Tunis, a spokesman at PLO headquarters called the end of the hijacking "a success for PLO diplomacy," Reuter reported.

Although it remains unclear exactly how the hijacking was carried out, one western diplomatic source here said the leader of the group, known only as Omar, had traveled on the liner several times and had befriended the captain.

Quoting a report from the Qatar New Agency, the diplomat said the man posed as an agent for a Greek shipping line, and thus was able to gather information to plan the hijacking.

It is also unclear exactly who the terrorists are but they claimed in broadcasts Tuesday to be members of the Palestine Liberation Front. That organization has splintered into three parts, one of them still allied to Arafat and the other two opposing him. Abbas, one of the Palestinians who took part in today's negotiations, heads the faction loyal to Arafat.

The chief demand of the hijackers had been the release by Israel of 50 Palestinians imprisoned there on terrorist charges.

The Egyptian government said that negotiations began about 7:15 a.m. local time (1:15 a.m. EDT) today, as the ship lay outside Egyptian territorial waters, about 16 miles north of here.

"In order to preserve the lives of the passengers, authorities agreed to negotiations," the Egyptian statement said. "At 4:20 p.m., the hijackers, whose number is four, agreed to surrender without preconditions. They surrendered at 5 p.m." The statement did not say what was done with the hijackers.

Italian police and judicial investigations indicate that the four hijackers most likely joined the cruise in Genoa. The Achille Lauro departed from there Oct. 3 on what was to be a 10-day cruise of the Mediterranean, with stops in Naples, Sicily, Egypt, Israel and Greece, Jenkins reported from Rome.

Crewmen and several passengers who had left for the land tour of Egypt shortly before the ship was hijacked Monday have spoken of four young men, all in their early 20s, who boarded the ship in Genoa and occupied cabin 82 during the voyage to Alexandria.

According to officials of the Flotta Lauro, the owner of the hijacked vessel, one of the men in cabin 82 had used the passport stolen from a 23-year-old Argentine with the last name of Zarlenga in Rome in July. His companions, according to the company records, had passports with the following identities: Antonio Alonco, 20, of Argentina; Franco Jados, 20, of Canada, and Stale Wan, 20, of Norway.

The four men reportedly remained apart from the rest of the cruise passengers and did not appear to fit into the ship's cruise routine. Several passengers said that the "Norwegian" did not appear to speak Norwegian or English and all four had dark complexions and could have been Arabs.

Although Col. Antonio Passaro, of the Genoa port police, has adamantly defended customs and boarding procedures on the ship last week and declared that "all documents [of the passengers] appeared to be in order," the speculation among the police is that the four boarded with stolen passports, smuggling on their guns and explosives in the crush of cruise passenger baggage.

Italian Prime Minister Craxi said the Italian government had mobilized politically and militarily to try to free the hostages.

"In my own mind I set a deadline. We would have had to do something tonight," he said.

But he said the government had concentrated on political and diplomatic efforts because it knew that any military move in an "extreme" case could involve the loss of life of Italian troops, the ship's crew members, who were mostly Italian, and innocent passengers.

In the end, Craxi said, what won the day was the "political and factual isolation of the terrorists," who he said apparently had found no support either from the Palestinian mainstream headed by Arafat or from such radical Arab governments as Syria, which refused yesterday to allow the hijacked liner into its territorial waters when it sought to dock at Tartus.

Craxi expressed thanks to the governments of Egypt, Tunisia, Syria and Cyprus for their help in resolving the crisis. He had specific praise for Arafat, for dissociating his group from the hijacking, then helping to negotiate the pirates' surrender.

"We want to thank the president of the PLO, Yasser Arafat, who expressed his condemnation of the hijack and helped to seek a solution," Craxi said, adding that it was Arafat's envoys who persuaded them to give up on condition they would be allowed to go to a still undisclosed country.

Italian Foreign Minister Giulio Andreotti said Italy had been told yesterday morning that it not need fear for its citizens on board the vessel because the hijackers had nothing against Italy, which for the most part has followed a pro-Arab foreign policy in recent years that has greatly angered Israel at times.

"I don't think the hijackers particularly opposed Italy, since the first messages Monday morning said the Italians on board could consider themselves safeguarded," Andreotti said tonight.

"Probably they thought that a cruise ship with no weapons on board, with many foreigners, among them many Americans, some of Jewish origins, could be a good target for pressure," Andreotti speculated.

Until late tonight, there had conflicting reports about Klinghoffer's fate, with Egyptian and shipping officials here insisting that their information indicated no one had been killed.

In Cairo, news of the surrender and the early indication of safety of the passengerswas greeted with elation and relief.

Frank Hodes, whose wife, Mildred, and his sister, brother-in-law and cousin were aboard the ship, said he felt that the past two days "were like forever."

"We've been married 43 years," Hodes said, minutes after receiving the news of his wife's release. "She's my life. I just hope she's not too distraught over this terrible experience."

Most of the 734 passengers had left the Achille Lauro in Alexandria, Egypt, for a day trip to the pyramids before it was hijacked.