A British warship shot down two Skyhawk fighter-bombers taking part in the first Argentine air attack in more than a week on the British naval task force near the Falkland Islands, the Ministry of Defense said tonight.

Ministry spokesman Ian McDonald said the planes were shot down by Sea Wolf missiles in the first combat use of the advanced British weapons that are designed to destroy missiles or aircraft. He said several Argentine sorties were flown against the task force, but the fleet suffered no damage or casualties.

In Buenos Aires, the military command confirmed the loss of two warplanes but said that the planes had "considerably damaged" two British frigates, correspondent Jackson Diehl reported. The British warships had been shelling the Falklands capital of Stanley when the Argentine planes attacked, the command said. It added that Argentine forces also today shot down a British Sea King helicopter near Stanley.

McDonald announced that a Sea King helicopter from the fleet was forced to ditch into the South Atlantic, in a "separate, unrelated incident" to today's hostilities and that all four crew members had been rescued. There was no evidence, he said, that the loss was caused by Argentine action.

At the United Nations, Secretary General Javier Perez de Cuellar met for the sixth day with diplomats from the two countries seeking to negotiate a settlement to the South Atlantic conflict, special correspondent Michael J. Berlin reported. Despite what he called a "favorable reaction" from Argentina on the question of sovereignty over the islands, the secretary general said Wednesday night he was still "seeking clarifications" from both sides on that issue and others.

In the past, Buenos Aires has insisted that any settlement include a guarantee of eventual Argentine sovereignty. But Argentine deputy U.N. representative Jorge Herrera Vegas said Wednesday, "We can only report that sovereignty is not a precondition to the negotiations. It is our objective, not our precondition, and no one can deny our right to have that as an objective."

British U.N. Ambassador Anthony Parsons was to meet with Perez de Cuellar Thursday morning, bringing London's answer to what he called the "very interesting proposals" by Argentina. Britain has insisted that any agreement state clearly that final sovereignty over the disputed islands not be prejudged.

Argentine Foreign Ministry officials in Buenos Aires cautioned Wednesday that optimistic reports about the prospect of an accord could soon evaporate. "Nothing has changed--it could go either way," a high government official said. Other government sources said Argentina had made no new concessions in its basic position, although a series of new proposals had been submitted to Perez de Cuellar.

Today's action, the third straight day of fighting after a four-day lull, began when three Argentine Skyhawks attacked a British warship, defense spokesman said.

"Two were shot down. The other escaped," McDonald said. He did not say whether any British aircraft were used in defense. The action took place in thick fog off the islands, seized by Argentina April 2.

The attacks marked the first time in the 12 days of hostilities around the Falklands that Argentina has deployed its A4 Skyhawks, American-built warplanes of Vietnam War vintage. Argentina is believed to have about 90 of the bomb-carrying planes, most of them land-based, in the southern part of the country.

Since the country's lone aircraft carrier, the 25th of May, also carries Skyhawks, their use could mark the first action for the Argentine carrier. The British Ministry of Defense, emphasizing that it had only received first reports, did not say whether the attackers were land- or carrier-based.

The Skyhawk can carry about 5,000 pounds of weapons and has a combat range of 460 miles without refueling--just enough to reach the Falklands from the mainland and return.

The Defense Ministry did not identify the ship that was attacked nor indicate whether the same ship downed the Skyhawks. However, only two ships in the task force, the frigates Broadsword and Brilliant, are equipped with the Sea Wolf. They normally provide antimissile cover for the two aircraft carriers in the armada of more than 70 ships.

The incident, reported to have taken place about 20 to 30 miles off the Falklands, marked the first Argentine air attack on the fleet since a jet firing a French-built Exocet missile demolished the destroyer Sheffield eight days ago, killing 20 crewmen. Unlike the frigates, the 4,100-ton Sheffield was not equipped with Sea Wolf missiles.

The Argentine military command also acknowledged Wednesday that one of its Puma helicopters had been downed by the British Sunday. A military communique said the helicopter was shot down by British planes while attempting to rescue survivors from the fishing boat Narwal, attacked and seized by the British.

Argentina has carried out three separate air attacks on the British fleet and has reportedly lost at least six aircraft.

Despite bad weather, the Defense Ministry said antisubmarine patrols by air have continued, some flown by Nimrod reconnaissance planes from Ascension Island, 3,500 miles to the north. The planes have been fitted for aerial refueling and today's announcement was the first disclosure that they are now operating over the Falklands.

Special correspondent Berlin reported the following from the United Nations:

British Ambassador Parsons emerged from a 90-minute meeting with Perez de Cuellar saying only, "I've had a very detailed discussion of a number of points of substance with the secretary general."

The British remained cautious about the prospects for agreement on all the outstanding issues. They expressed fears privately that the Argentines, having demonstrated some flexibility on sovereignty, might now make unreasonable demands on other aspects of the agreement, and thus wreck the talks while escaping the blame.

Argentina's Herrera Vegas expressed the hope that the British "will show the same flexibility we have shown and will make some concessions."

The secretary general said tonight, "I still feel perhaps at the end of the week we might have some clearly positive results."