The Palestinian accused of killing American Leon Klinghoffer aboard the hijacked cruise liner Achille Lauro today denied having confessed to the crime to investigating magistrates.

The Palestinian, 23-year-old Yousef Magid Molqi, told an astonished court that as far as he knew, Klinghoffer was not even aboard the Italian ship when he and three other Palestinians hijacked it off the coast of Egypt last October.

Molqi, testifying for the first time before the court that is trying him and 14 other Arabs for either direct involvement or complicity in the hijacking and murder, said that if he had signed a confession he did not then know what was in the statement because he was tired or drugged.

"I didn't know what was put in the statement, I was tired," Molqi said through a translator after Judge Lino Monteverde had read a long passage from his confession. "It happened in the evening. I was given injections to sleep."

Molqi's efforts to retract his confession came as telephone callers in Greece and Lebanon threatened the Italian judiciary and Italian interests in Italy and abroad because of the trial, which began here yesterday, in the cruise liner's home port.

The warnings came after a bomb exploded in front of the fifth-floor office of the Italian Chamber of Commerce in Athens and another was found unexploded at the Italian Consulate outside the Greek capital. Two persons were slightly wounded in the blast.

While the telephoned threats in Greece were anonymous, those in Beirut claimed to speak in the name of Mohammed Abbas, leader of the Palestine Liberation Front faction of the Palestine Liberation Organization. Prosecutors have charged Abbas with organizing and directing the hijacking and he and some of his aides are being tried in absentia .

"The fascist Italian judiciary will take its share of retaliation despite any security precautions," the Beirut caller said.

Italian prosecutors have concluded that PLO chairman Yasser Arafat did not know of the hijacking, and that Abbas staged it in part to challenge Arafat's leadership.

Today, however, it was Molqi who dominated the proceedings with his retractions, contradictory statements, evasions and defiant insistence he was nothing but a soldier following orders in the Palestinians' struggle to get their homeland back from Israel.

His performance did not awe Judge Monteverde, the president of the two-judge, six-juror court.

"You have given seven different versions of events," Monteverde said shortly after he started grilling the defendant in the heavily guarded basement courtroom where the five defendants in Italian custody sit in steel cells lined with bulletproof glass. "Which version do you confirm today?"

Asked bluntly if he had not confessed to killing Klinghoffer, an elderly wheelchair-bound passenger, Molqi replied:

"No I didn't kill him. This is not true. He wasn't even on the ship. I did not see him. I think this is a frame-up by the Americans and the Syrians."

The judge then read him an excerpt from his signed confession in which he had said: "It is true. I killed the American passenger. . . I shot twice, once to the head, once to the chest."

Molqi said simply, "Those are not my words."

Judge Monteverde then read another excerpt in which Molqi said he chose Klinghoffer for execution after Syria refused to allow the ship to stay in Syrian waters off the port of Tartous with more than 400 passengers and crewmen -- hostages the hijackers wanted to exchange for 50 Palestinians held by Israel. "I chose Klinghoffer," the judge read, "so that everyone would know we would have pity on no one."

Molqi again denied those were his words, even after the exasperated judge said they had been confirmed by the testimony of witnesses who had seen him order Klinghoffer wheeled to the rear of the ship, where he was killed, and from two crewmen who were later forced to dump the body and wheelchair overboard.

The hijacking came to an end after two days when Abbas, claiming to be a mediator for Arafat, talked the hijackers into surrendering in Egypt. U.S. Navy jets intercepted the Egyptian jetliner flying them to Tunisia, where Arafat had promised to try them in a PLO court.

Their plane was forced down at the Sicilian NATO base at Sigonella, where Italian authorities arrested them -- but let Abbas leave the country, saying there was no proof of his complicity.

Along with Molqi, two other hijackers, Ibrahim Abdellatif Fataier and Ahmad Marouf Assadi, are being tried here. The fourth, Bassam Asher, is to be tried in a juvenile court, as he was only 17 years old at the time of the hijacking. The other defendants in the court are Mohammed Issa Abbas, the Palestinian Liberation Front leader' cousin, who has been convicted of bringing into Italy the guns and hand grenades used by the hijackers and Mowefaq Gandura, about whom not much is known, but who is accused of providing financing for the hijackers.