Italian magistrates investigating the slaying of American hostage Leon Klinghoffer now say they believe that the principal goal of the terrorists aboard the Achille Lauro was the hijacking of the cruise ship and not, as the four Palestinians said following their capture, sea transport to the Israeli port of Ashdod to carry out an attack there.

This interpretation of events by Italian investigators is shared by the captain of the Achille Lauro, Gerardo de Rosa, who said in an interview aboard the ship today that after the hijacking he was struck by the terrorists' "unhesitating choice" to sail to Tartus, Syria, where, he said, they clearly expected some sort of support.

De Rosa said the one terrorist he had talked with regularly in English had given the impression that the hijackers initially planned to leave the ship in Tartus, taking with them the American and British passengers, presumably as hostages.

The first suggestion that Ashdod, the cruise ship's next scheduled stop after Egypt, was the actual target of the operation came from Israeli officials on Oct. 9, the day the hijackers surrendered. But the Israelis offered no direct evidence.

That night, sources close to the Palestine Liberation Front, to which the hijackers belong, were reported to have said in Cyprus that an attack in Israel was the goal and that the ship should not have been hijacked.

Italian investigators said today that this version also has been given by the four hijackers awaiting trial here. But Genoa deputy prosecutor Francesco Meloni said the four appeared to have come up with the story after talking with Mohammed Abbas, the PLF leader who helped negotiate their surrender.

Meloni said the principal reason that investigators both here and in Syracuse, in Sicily, now believe that the hijacking alone was the goal is "the extreme difficulty the terrorists would have encountered in trying to carry out" an attack at Ashdod. He said this was based on the Italians' supposition that Israeli security would be too tight for them to do anything.

It was also thought that investigators here were basing their beliefs on interrogation of Mohammed Zainab, a Palestinian arrested here 10 days before the hijacking for carrying forged identity documents. After the hijacking, authorities questioned Zainab, and there are unconfirmed reports that he has admitted involvement but spoke only of a hijacking, not of an attack in Israel.

Meloni also said today that questioning of the ship's crew indicated that earlier accounts of the terrorists' being discovered with weapons and then deciding to hijack the ship were incorrect.

Meloni, who, with three other investigating magistrates, interviewed more than 400 persons aboard the Achille Lauro, said today that an account of a waiter discovering the terrorists cleaning their weapons and thereby inadvertently causing the hijacking was untrue.

That account also was denied by de Rosa, other ship officials and Fausto Vignani, the Lauro shipping line's director general.

De Rosa, in the interview, would not say whether there had been any eyewitnesses to the killing of Klinghoffer, whose body washed ashore in Syria this week. But he said that the ship's barber, Ferruccio Alberti, and a Portuguese sailor had been forced by the hijackers to throw Klinghoffer's body overboard.

The growing complexity of the case makes it clear that the investigation will be a long one, and Meloni said there is no possibility that a trial can begin soon.

Meloni said investigators in Syracuse at first had believed the terrorists' story of an accidental hijacking but had changed their views when they decided that tight Israeli security measures at Ashdod would have made it impossible for disembarking passengers to take machine guns and explosives ashore -- unless their intention was simply to attack at the dock.

Italian sources said the Palestinians may hope that by denying they ever planned to hijack the Achille Lauro they will be treated more leniently by the Italian courts, Reuter reported.

Meloni said that the Syracuse magistrate initially had contemplated citing Abbas as a witness to help identify the hijackers, but that this was unnecessary after several of the American hostages, including Klinghoffer's widow, Marilyn, were brought to Syracuse to identify them.

He added that if the hijackers "provide us with even minimum evidence that Abbas had a greater role, the whole thing could change" and Italy could seek to cite him.

Meloni and other magistrates would not comment on who might have been the principal organizer of the hijacking. But Meloni said considerable interest was focusing on a fifth Palestinian believed to have been on board, traveling under a false name, who left the ship abruptly at Alexandria, Egypt, a few hours before the hijacking.

Aboard the Achille Lauro, where final preparations were being made today for this afternoon's departure on a new cruise, with de Rosa again in charge, the atmosphere was one of calm. Hundreds of passengers, including many West Germans and Italians, milled around the lower decks, apparently oblivious to the presence of five FBI agents who boarded the ship this morning for an independent investigation. But more than a third of the scheduled passengers reportedly had canceled their bookings.

On the bridge, talking with reporters, de Rosa said that following their decision to sail to Tartus on the morning of Oct. 8, the day after they seized the vessel, the hijackers appeared ebullient, replying to his queries as to whether they expected help from their "brothers" by saying excitedly, "You will see, you will see."

De Rosa said that the hijackers were constantly sending and receiving radio messages but that he could not understand them as they were in Arabic.

Later that day, he said, the hijackers' mood changed; they appeared disappointed and became upset and agitated. "That was when I became afraid," he said, adding that it was at this point, in the early afternoon, that the hijackers said they had killed Klinghoffer. It was also during this period that Syria refused the hijackers' requests to let the Achille Lauro dock.

"Then they began to seem unsure of themselves," de Rosa said. "Finally, they told me to head for Libya, but for a point far from Egyptian shores. But when we were about at Cyprus they got another radio message that made them become happy again, and they told me to head for Port Said."

He repeated his previous statements that after the hijackers had left his ship he had not immediately reported Klinghoffer's death because he was not entirely sure anyone had been slain. "At that point for me he was just a missing person," he explained, adding that another reason for the delay was the confusion that prevailed aboard when the hijackers finally left.