Italian Prime Minister Bettino Craxi resigned today after defending his government's actions in the aftermath of the hijacking of the cruise ship Achille Lauro and expressing dismay and bitterness at U.S. criticism of those actions.

President Francesco Cossiga accepted Craxi's resignation but asked his coalition government, which had been one of the most stable in postwar Italian history, to stay on in a caretaker capacity pending Cossiga's consultations with party leaders about the designation of a new prime minister.

Italian analysts believe that ultimately Cossiga will ask Craxi, as the most likely candidate to put together a new coalition, to try to form a new government.

In defending himself today before Parliament, Craxi added new details of the tense moments the hijacking caused in the traditionally warm relations between Italy and the United States.

He said that not only did the United States force the landing of an official Egyptian plane, with the hijackers and Palestinian official Mohammed Abbas aboard, on Italian soil after U.S. Navy jets intercepted it in the air, but, without Italian permission, it also landed two C141 military transports full of Delta Force commandos in its wake at the joint Italian-American Sigonella air base.

The Delta Force commandos, Craxi said, were under the orders of a U.S. Army general and were charged with taking the hijackers and Abbas forcibly from Italy to stand trial in the United States. The commandos stood down only after a conversation between Craxi and President Reagan early Friday morning after Craxi insisted that the hijackers, having committed crimes aboard an Italian ship, would have to stand trial in Italy.

Even after that, Craxi said, the U.S. violated Italian airspace by sending two of its military jets to trail the intercepted Egyptian airliner after it was ordered flown under the escort of four Italian fighters from Sicily to Rome.

Sources close to the prime minister said the escorts had been ordered out of fear that the United States would again try to intercept the jet carrying Egyptian officials, armed escorts, Abbas and another official of the Palestine Liberation Organization.

"The Italian government has decided to open an investigation" of the action, Craxi said, "and a protest was immediately filed with the Washington government."

Craxi's five-party coalition collapsed as a direct result of the pullout of the small, pro-American Republican Party and in the aftermath of sharp U.S. criticism of Italy's role in the release of Abbas, a senior Palestinian official accused by the United States of masterminding the hijacking.

Craxi, a Socialist whose government was just 29 days short of being the longest-lasting Italian government since World War II, officially submitted his resignation after delivering a lengthy defense to Parliament of his government's actions last week.

Craxi described Italy's overall actions as a "great success" -- despite the death of Leon Klinghoffer, a 69-year-old American passenger -- because many more people might have died had there not been a negotiated end to the hijacking.

The prime minister said the U.S. criticism of his handling of the hijacking and its aftermath, coming from an ally, "could not but provoke the strongest and displeased surprise as well as a feeling of bitterness."

The collapse of Craxi's government became inevitable yesterday when Defense Minister Giovanni Spadolini, the head of the Republican Party, announced that he and the two other Republican ministers in the government were resigning. He said that they were leaving the government because of Craxi's handling of the hijacking of the ship and his failure to consult with his coalition partners during the height of the crisis with the United States over its demands for the extradition of Abbas.

In his 40-minute speech to Parliament today, Craxi criticized the "polemical tone" of the U.S. reaction and said that the words spoken against his government in Washington could be derived only "from an incomplete assessment of the facts and the circumstances" that dictated his government's actions.

He again defended the legal grounds on which he allowed Abbas to leave Italy Saturday despite strong demands from Washington that he be "provisionally" arrested pending extradition.

Craxi said Abbas was allowed to leave Italy after Italian judicial officials had ruled that Washington had failed to supply Italy with the minimum proof required under Italian law for Abbas to be detained. He reiterated that Abbas also had been protected by diplomatic immunity and by the Egyptian government, which had insisted that Abbas, as a passenger in their official plane, be freed.

Craxi said that even though Defense Minister Spadolini maintained that his reason for abandoning the government was the lack of consultation before the decision was made to let Abbas leave, Spadolini had been personally informed Saturday that Italian judicial authorities could find no reason to hold Abbas on the basis of U.S. evidence. Craxi said that the Republican leader had in effect agreed, so long as the four hijackers had been positively identified before Abbas left the country, which they were. The four are now jailed in Italy.

As to accusations that Italy had shown itself soft on terrorism in the affair, Craxi said, "No government in the free world has been able to gain as decisive results in the war on terrorism without destroying the principles and rules of its state of law as has the government of the Italian Republic."

The implication was that Italy was not prepared to resort to extra-legal means to fight terrorism as other nations, including the United States in the Achille Lauro affair, had done.

Meanwhile Italian forensic experts, with a U.S. medical examiner in attendance, conducted an autopsy here on the body of Klinghoffer, which washed ashore in Syria Sunday.

Italian sources close to the procedure said today that the initial examination of the body confirmed Syrian reports that Klinghoffer had died of two bullet wounds, one to the head and the other to the chest.