U.S. Navy carrier planes and Libyan fighters had more than 25 encounters over the Mediterranean Sea yesterday, none of them hostile or within what Libyan leader Col. Muammar Qaddafi claims as his territorial airspace, Defense Department officials said.

The number of U.S. intercepts was unusually high and came as Libya increased its force of Soviet-supplied SA5 antiaircraft missiles at Sirte on the Gulf of Sidra.

Qaddafi claims as Libyan territory all of the gulf, which borders Libya. The United States regards as international waters the area beyond 12 miles from shore.

U.S. fighters making the intercepts yesterday flew from the carriers USS Coral Sea and USS Saratoga as part of flight operations that began at 7 p.m. EST Tuesday and are scheduled to end Saturday, according to the Pentagon.

Navy fighters fly between their carriers and foreign planes, a tactic designed to screen the carriers and to position Navy planes to down enemy aircraft before their weapons are in range of U.S. ships.

While the Pentagon did not say so, its assertion that no hostile encounters occurred indicates the Libyan pilots let themselves be shouldered away before nearing either carrier's battle groups.

Pentagon officials said the intercepted Libyan planes were Soviet-supplied MiG23 Flogger and MiG25 Foxbat fighters, French Mirage F1 interceptors and a Soviet transport. The Libyan planes flew in two-aircraft formations in most instances, officials said.

"These were routine intercepts," said a Pentagon official, who declined to be identified.

The two carrier task forces are conducting highly visible operations north of the gulf in hopes of notifying Qaddafi that his support of terrorist operations could cost him dearly, administration officials said.

The Joint Chiefs of Staff have developed plans for the bombing of several targets in Libya, officials said, but have recommended against striking any of them because none is directly linked to a specific terrorist act.

However, officials said, President Reagan might order retaliatory action if Libya tries shooting down a U.S. plane or launching one of its 12 SA5s at Sirte.

When Qaddafi learned that the USS Saratoga was steaming through the Suez Canal to join the USS Coral Sea in the central Mediterranean last month, officials said, he urgently requested more Soviet technicians to help finish SA5 sites. Besides putting a dozen missiles on launchers, they said, the Soviets have helped install improved surveillance radar there.

Qaddafi has threatened to attack U.S. ships crossing a "line of death" he has drawn atop the gulf at 32 degrees, 30 minutes north latitude.

U.S. officials said no Navy ships or planes crossed that line last month or in the current exercises. But the line will be crossed eventually, they said, to reassert the U.S. position that its planes and ships can use what it considers international gulf waters.

One official predicted that the crossing will come next month when the carrier USS America is to join the other two carriers.

Qaddafi also has threatened to intercept Israeli aircraft to retaliate for Israel's forcing down Feb. 4 of a private jet that took off from Libya. U.S. officials said they have detected no sign that Qaddafi has tried to interfere with Israeli flights.