The hit-and-run attack by British Marines on an Argentine military outpost on tiny Pebble Island Friday night and Saturday morning inflicted heavy casualties on Argentine troops and destroyed warplanes and possibly a radar installation, according to British reports today.

Correspondents who watched from a destroyer that shelled the island during the raid described a classic, precisely run operation. One hundred Royal Marines landed on the island and escaped with no serious casualties after fierce fighting in predawn darkness illuminated by moonlight and gunfire.

The commandos, led by a major, landed from helicopters on a clear night miles from the 600-yard airstrip on the small island just north of West Falkland Island. Argentine forces reportedly were using the airstrip as a "stepping-stone" base for moving supplies and troops around the Falklands, a hiding place for Pucara ground attack planes that could menace a British invasion force and a mobile radar station that could help direct Argentine air strikes against the British fleet.

The British correspondents reported that the commandos took hours to make their way by foot over the island's rocky, mountainous terrain to predetermined positions near dug-in Argentine defenders. Meanwhile, the British destroyer, which was not identified, left the rest of the task force after nightfall Friday to rendezvous with the commandos early Saturday morning.

"There was a bright moon, and the shoreline and mountains behind it were clearly visible," said British commercial television correspondent Michael Nicholson.

Arriving at the Argentine encampment around the Pebble Island airstrip with the commandos was a naval gunfire spotter, according to the destroyer's captain. He used a radio to direct pinpoint shelling of Argentine positions around the airfield by two of the ship's 4.5-inch guns.

"The bombardment was spread over a large area of hillside where the force commander believed the Argentine forces were dug in," the destoyer's captain, who was not identified, told British radio and television correspondents in an interview today. "We spread the fire up the hillside to keep their heads down."

Under cover of this bombardment, some of the commandos machine-gunned Argentine positions while others placed and detonated explosives that blew up camouflaged aircraft and other equipment and installations. The British Defense Ministry said 11 planes were destroyed, including a short-takeoff transport plane and six Pucaras. A large ammunition dump also was blown up, the ministry said.

British sources said the Argentine forces on Pebble Island were believed to have suffered heavy casualties. The Defense Ministry said it had no reliable information on this.

The British correspondents said the sky was lit up by the naval bombardment, by flares fired from the ship at the commandos' request and by machine-gun and mortar fire in combat between the British Marines and Argentine troops.

"The battle exploded in front of me as I watched from the destroyer just offshore," reported British Broadcasting Corp. correspondent Brian Hanrahan after he returned to the task force flagship, the aircraft carrier Hermes.

"From the sea, the ship threw out orange flames and covering fire, then star shells to show the attacking forces the ground. Then salvo after salvo of high explosive shells each whined away through the darkness to land among the defenders."

The destoyer fired 100 shells in 30 minutes. Half an hour before dawn, the captain decided to rejoin the task force before the destroyer became a daylight target for Argentine warplanes.

As the commandos fought their way to waiting helicopters that took them back to the task force, two suffered concussions from land mines detonated around the airstrip by Argentine forces by remote control, the British correspondents said. The Defense Ministry said the Marines suffered only "minor" injuries.