The U.S. downing of two Libyan fighter jets drew a chorus of international criticism, with Arab nations denouncing it as a "dangerous act of aggression," Moscow calling it "state terrorism" and Moslems in Beirut warning it could affect 15 foreign hostages held in Lebanon.Britain reacted cautiously to the Wednesday dogfight over the Mediterranean, while other European allies expressed concern the incident would escalate tension in the region. Italy swiftly boosted security operations by its navy and air force.

"News that Washington's anti-Libyan campaign had produced an armed clash over the Mediterranean, as a result of which two Libyan planes were brought down, has been received with indignation in Moscow," Foreign Ministry spokesman Gerasimov said at a news conference Thursday.

"Such actions, being as they are a show of political adventurism and state terrorism, may bring about serious consequences," he said.

"Irrespective of pretexts, the use of force contradicts international law, runs counter to the efforts of the world community to find political solutions to the existing conflict situations," Gerasimov said.

In Moscow, Soviet Foreign Ministry spokesman Yuri Grimitski said Wednesday that recent American threats against Libya may stem from opposition within some circles in Washington to the new U.S. dialogue with the Palestine Liberation Organization.

"I believe someone just does not like the beginning of a U.S.-PLO dialogue and the process of moving the Arab-Israeli conflict out of stagnation," the Soviet spokesman said.

PLO Chairman Yasser Arafat, whose renunciation of terrorism and recognition of Israel's right to exist led to the U.S. decision last month to open talks, appeared surprised upon hearing of the incident while on a visit to Egypt.

"It is a very serious matter. It will reflect negatively on the whole process," Arafat said in a broadcast on the Cable News Network from Cairo after talks on prospects for peace in the Middle East with Egyptian President Hosni Mubarak.

Libyan leader Moammar Gadhafi denounced the incident as an act of "official American terrorism" and was joined by Iran in harshly condemning the United States. Both countries claimed the incident was a prelude to more U.S. military attacks on Libyan targets.

A Lebanese Moslem militia official in Beirut, who requested anonymity, warned the development would reflect "negatively" on the fate of 15 foreign hostages held in Lebanon. Nine Americans are among the captives.

"We have learned from past experiences that mounting tension in the region reflects negatively on the hostage issue," he said. "This time it will not be different."

Defense Secretary Frank Carlucci said two U.S. jet fighters "acting in self-defense" shot down a pair of Libyan MiG-23s over the Mediterranean Sea Wednesday when the Libyans sped toward them "in a hostile manner." The Libyan pilots apparently parachuted from their crippled Soviet-built jets.

Israeli Prime Minister Yitzhak Shamir's office said based on Libya's past behavior, Israel had no reason to question the U.S. account of the incident and that Israel had "no connection to it whatsoever."

Two weeks ago, President Reagan said the United States and its allies had discussed possible military action against a reported Libyan chemical weapons plant, but U.S. officials insisted the latest incident had nothing to do with the presence of the factory.

Chedli Klibi, secretary-general of the 22-nation Arab League, described the downing of the Libyan jets as "an extremely dangerous act of aggression."

Klibi urged the United States to stop "provocations" near the Libyan coast.