One of the four hijackers of the cruise liner Achille Lauro has told investigators that Mohammed Abbas, the leader of the Palestine Liberation Front, was, as U.S. officials claim, the mastermind behind the hijacking, according to Italian newspaper reports.

Judicial officials here and in Genoa, where the main investigation is being conducted, refused to confirm or deny the reports that one of the Arab hijackers was cooperating with investigators.

Judicial authorities here, however, did confirm that one of the four hijackers had been transferred to a new jail near Genoa from the maximum security prison at Spoleto. They had been jailed there 10 days ago after being flown from Sicily, where the Egyptian airliner carrying them had been forced down by U.S. Navy jets.

The Italian newspaper stories, all quoting unidentified unofficial sources, said that one of the four hijackers had identified Abbas as the military commander of the hijacking and said that before the four were turned over to Italian custody, Abbas promised he would see that they would be freed somehow.

The almost identical stories appeared this morning in the moderate Milan daily Corriere della Sera, the left-of-center La Repubblica and L'Unita, the official newspaper of the Italian Communist Party.

The stories alleged that the hijacker had told investigators that Abbas promised even to stage terrorist attacks in Italy if that was what was needed to gain their release from Italian custody.

Reached by telephone tonight, deputy state prosecutor Francesco Meloni, in charge of the interrogation of the hijackers, refused to confirm or deny the newspaper stories.

The revelations, if true, seemed certain to complicate the efforts of caretaker Prime Minister Bettino Craxi to form a new government.

Craxi was forced to resign last week when his 26-month-old coalition government collapsed after Defense Minister Giovanni Spadolini's Republican Party pulled out of the coalition because Abbas was allowed to leave Italy despite U.S. demands for his extradition.

Both U.S. and Israeli officials have claimed that Abbas masterminded the hijacking of the Achille Lauro, in which an elderly U.S. passenger, Leon Klinghoffer, was killed and thrown overboard.

Craxi defended his government's decision to allow Abbas to leave the country 10 days ago, contending that the U.S. government had failed to present evidence that would have allowed Italian courts to order his provisional arrest pending the U.S. extradition request. The United States argued that it had provided "convincing" evidence.

Craxi said he did not know whether Abbas was guilty but that under Italian law there was no ground to hold him.

Spadolini withdrew his party's three Cabinet ministers two days after Abbas left the country, protesting that the Republican Party, one of five in the coalition, had not been consulted.

President Francesco Cossiga asked Craxi last weekend to try to form a new government. Before he left for New York today, Craxi held preliminary consultations with political leaders about putting together a new five-party coalition.

The success of that hinges largely on the Republicans' willingness to serve again under Craxi. Spadolini has made it plain that he would join a new Craxi government only if Craxi agrees to greater sharing of decision making, redefines his foreign policy and reaffirms Italy's traditional ties with Washington.

Even before the hijacking there had been tension between Craxi and Spadolini over the government's foreign policy in the region -- one that sought to weld alliances between Italy and Arab nations on the Mediterranean to try to influence a resolution of the Middle East conflict. Spadolini, a noted Atlanticist with close ties to Israel, repeatedly attacked such a policy as being too pro-Arab and not in line with U.S. policy in the region.