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, Defense Secretary Frank Carlucci said.

The Navy F-14 Tomcats fired four missiles, knocking the MiGs out of the sky over international waters 70 miles north of Libya's coast, and then returned safely to the aircraft carrier John F. Kennedy some 127 miles north of the coast, Carlucci said at the Pentagon six hours after the 3 a.m. MST incident.The Libyan pilots apparently parachuted from their crippled Soviet-built jets, and Libya launched a search and rescue mission, Carlucci said.

Carlucci, with Navy Adm. William Crowe, chairman of the Joint Chiefs of Staff, told a news briefing in Washington that U.S. jets and ships were conducting routine training maneuvers in the Mediterranean when the incident occurred at about noon local time north of Tobruk, Libya.

Repeatedly emphasizing that he was offering information based on "preliminary reports," Carlucci also insisted the Navy action had nothing to do with the presence of what the United States says is a chemical weapons plant in Libya.

"There was no way that the Libyans could have interpreted our evasive maneuvers as hostile intent," Carlucci said.

The incident, however, became the latest in a series of clashes between the United States and the North African nation led by Moammar Gadhafi, including the U.S. bombing of the Libyan cities of Tripoli and Benghazi April 15, 1986.

Carlucci said he did not know if a verbal warning was issued by the pilots, though that is standard practice before engaging in combat, when the MiGs accelerated toward them. But he said, "(We) maneuvered to avoid the closing aircraft . . . (yet they) continued to close in in a hostile manner."

A Pentagon official who asked to remain anonymous said the MiGs had their fire control radar on, indicating they were prepared to shoot, when the Navy pilots acted. One MiG was brought down with a heat-seeking Sidewinder missile and the other fell to one of three radar-guided Sparrow missiles fired.

President Reagan, vacationing in California, was awakened and informed at 3 a.m. PST, an hour after the incident, according to spokesman Roman Popadiuk.

Army Lt. Gen. Colin Powell, the president's national security adviser, woke Reagan at his home in Bel Air, Calif. Failure to wake Reagan in August 1981, after a similar encounter between American and Libyan jets, had led to sharp criticism on Capitol Hill and elsewhere.

A White House spokesman said President-elect George Bush also was awakened Wednesday morning at his residence in Washington. Neither Reagan nor Bush had any immediate comment.

Libyan radio, monitored by the British Broadcasting Corp. in London, said Libya's foreign ministry accused the U.S. of a "premeditated" attack but did not dispute that the incident occurred over international waters. Gadhafi, however, reportedly declared: "(We) will meet challenge with challenge."

Popadiuk said in Los Angeles, "The F-14s were threatened while conducting routine operations in international airspace north of Tobruk. The F-14s returned safely to their ship, and two parachutes were sighted from the downed Libyan aircraft," indicating the Libyan pilots might have escaped.

Popadiuk said there were no reported injuries from the Kennedy, which headed for duty in the Mediterranean Aug. 2. The Pentagon announced Tuesday that a 12-ship battle group led by the Theodore Roosevelt, the newest nuclear-powered carrier, had departed for the Mediterranean Friday.

The Roosevelt left from Norfolk, Va., also the home port of the Kennedy, with 2,000 assault Marines and amphibious landing gear - heightening speculation about U.S. intentions in light of Reagan's revelation last month that his administration had discussed with NATO allies possible military action against the chemical plant in Libya.

A Navy statement, however, insisted the Roosevelt's departure was "a routine deployment" planned "many, many months ago" - and it has been almost three years since U.S.-Libyan tensions reached their peak in the spring of 1986.

On March 24, 1986, Libya fired missiles at U.S. jet fighters flying near the disputed waters of the Gulf of Sidra, and the United States retaliated by attacking a missile site and destroying two Libyan patrol boats.

Less than a month later, Libya became the target of the biggest U.S. air strike since the Vietnam War when Air Force planes hit Tripoli and Benghazi, killing 17 civilians and injuring 100.

The attack was in retaliation for a bombing of a Berlin disco popular with U.S. servicemen 10 days earlier. The United States charged at the time that Libya was behind the bombing, though later evidence indicated Syria was more likely the culprit.

The U.S.-Libyan encounter Aug. 19, 1981, involved two F-14s from the aircraft carrier Nimitz that downed two Soviet-built Libyan SU-22s with heat-seeking Sidewinders over the Gulf of Sidra. The Americans returned safely, but Libya said one Libyan pilot was found in the water and the other was missing and presumed killed.

Wednesday's incident occurred hundreds of miles away from the disputed Gulf of Sidra, which Gadhafi claims is Libyan territory. The United States claims most of the gulf constitutes international water.