The United States moved quickly yesterday to support Egypt in its storming of the hijacked Egyptian airliner in Malta, assuring President Hosni Mubarak in advance that it would act to stop Libya from interfering in any Egyptian military action and offering "all appropriate assistance," a U.S. official disclosed yesterday.

"We offered assurances to the Egyptians that we would not permit the Libyans to take any military actions," the official said. "If the Egyptians took any actions vis-a-vis the hijackers, we would not permit the Libyans to interfere."

The official also said the United States offered "all appropriate assistance" to the Egyptian and Maltese governments to end the hijacking, adding, "I would not exclude the possibility we provided equipment and expertise."

He refused to elaborate but did say that U.S. officials had been in continuous contact with Egyptian authorities at the Maltese airport of Luqa where the Egyptian airliner had landed.

The disclosure of the U.S. assurances to Egypt came shortly after Secretary of State George P. Shultz said Washington had worked "very closely and cooperatively" with Egypt to help it end the latest hijacking episode "as expeditiously and firmly as possible."

"The way to get after these people is to get after them with both barrels," Shultz said on NBC's "Meet the Press." He said terrorists "aren't worth the time of day. They're not even people, doing what they're doing."

Clearly pleased by Egypt's decision to storm the airliner, the State Department issued a statement shortly afterward commending it for its action as well as the Maltese government for its cooperation with Egyptian authorities. The statement was issued before the extent of the casualties was known.

Later, the department said: "The United States supports the difficult decision of the governments of Malta and Egypt to end the brutal terrorist hijacking of Egyptair Flight 648. The terrorists commandeered the aircraft and then murdered and wounded innocent passengers, including Americans. We are advised that at the time of the rescue, the terrorists detonated explosives which killed and wounded additional passengers.

"We are saddened by the tragic loss of innocent life resulting from this act of terrorism and extend our deepest sympathy to all those who suffered through this ordeal.

"Terrorism, by its very nature, rejects the values civilized peoples hold dear. Those who direct and support these despicable acts must know that we remain determined that justice be done. We call on the international community of nations to cooperate in ending this scourge against humanity."

Unlike last June's hijacking of a TWA airliner, the United States had a relatively small direct stake in the Maltese hijacking because only three Americans were aboard.

Shultz seemed particularly anxious to stress U.S. cooperation with Egypt in ending the hijacking. Relations between Washington and Cairo were severely strained after U.S. warplanes on Oct. 11 intercepted an Egyptian airliner carrying terrorists responsible for the Achille Lauro cruise ship hijacking.

He also said Washington had cooperated closely with Malta, Greece and Italy during the latest episode.

Asked about security at Athens airport, the plane's last stop before the hijacking, Shultz said it had been brought up to a "good international standard" after the United States made an issue of it in the wake of the TWA hijacking from there last June.

"Whether there has been any relaxation since that time, I can't tell you," he said. "It shows that the security system in Athens, or perhaps anywhere else, is not perfect."

Shultz refused to say whether the United States had been planning any military action on its own or in connection with other governments but insisted "no one should give any quarter, no place to hide for these terrorists." Shultz was cautious about implicating Libya, Egypt's chief Arab enemy, but did note that the hijackers had asked to see the Libyan ambassador in Malta and that 26 transit passengers from Libya had boarded the Egyptian flight in Athens en route to Cairo.

Egyptian authorities initially acted as if they thought Libyan leader Muammar Qaddafi was behind the hijacking, declaring a state of emergency in the western desert region bordering Libya. The Libyans have reportedly been behind a number of recent terrorist activities directed against the Mubarak government or Libyan opposition leaders based in Cairo.

The link between the hijackers and Libya, if any, remained obscure last night. At least two of the hijackers carried Moroccan passports and a third either a Moroccan or Tunisian one, administration sources said. But the Arab-speaking hijackers were reported to have spoken with a Syrian or Lebanese, rather than a North African, accent.