The sucessful attack of a British destroyer by a missile-firing Argentine jet fighter yesterday suddenly thrust the battle in the South Atlantic into a crucial new phase.

Sources here indicated that the Argentines were trying to throw everything they had at the British fleet in what could become the biggest sea battle in the month-long confrontation over the Falkland Islands.

At the same time, however, several officials said the attack on Britain's HMS Sheffield, one day after a British submarine sank an Argentine cruiser, could turn out to be "the cloud that might have a silver lining," as one official put it.

This official meant that because both sides in the escalating fighting have now been bloodied, the United States could have a new opportunity to try persuading London and Buenos Aires to stop the combat.

Late yesterday, Secretary of State Alexander M. Haig Jr. canceled a trip to New York City to meet here with British Ambassador Sir Nicholas Henderson. Haig had reached Andrews Air Force Base before deciding to return "to stay in touch with the Falklands situation at an extremely delicate and critical phase," the State Department said.

U.S. officials said the meeting was an attempt to "consult and conduct new exploratory talks" with London about attempts, not necessarily only by the United States, to "reestablish peace efforts." They did not elaborate on the source of the attempts.

Earlier in the day, administration sources said discussions are under way here about a new U.S. effort to gain a cease-fire, with the United States prepared to fly medical supplies and food to the Falklands and assume a presence on the islands while another attempt at a settlement is made.

On the other hand, if the Argentines manage to attack or sink other British vessels, officials here said the situation could become extremely dangerous, with the tempo of combat overcoming any chance to call a quick halt.

Concern was expressed privately on Capitol Hill that the war could spread to the Argentine mainland if the British decide to bomb military airfields there.

Officially, the State Department said it had nothing to add to the British announcement about the destruction of the Sheffield. "As was the case with the sinking of the Argentine cruiser, the General Belgrano, we deeply regret the loss of life. These additional casualties underscore the urgent need for an early and peaceful settlement of this tragic conflict in the South Atlantic," the department said.

Sources here said the attack on the Sheffield apparently was by a French-built Super Etendard jet fighter based on Argentina's only aircraft carrier, a British-built vessel now called the 25th of May. The jet is believed to have fired a French-built Exocet missile, but there was no official confirmation about the weapons involved.

American specialists also said they believe the attack on the Sheffield would induce greater British respect for Argentine military capabilities. While some of the bold talk by the British fleet commander in recent days after a string of relatively easy victories is viewed as "psychological warfare," some specialists here said the British had not heeded early U.S. estimates that the Argentines had formidable capabilities.

The primary Argentine punch rests with its land-based force of about 150 combat jets, vastly more than the 20 British Harrier jump jets with the Royal Navy around the islands. The Argentines also have about 15 strike aircraft on their carrier.

On the other hand, U.S. specialists said Argentine maintenance of its planes, especially the 80 or so U.S. A4 attack jets, declines markedly the more the planes are used.

Last night, sources said there are indications that Argentina is attempting a major strike on the British fleet.

Officials with access to U.S. intelligence information predicted the British ships would scatter rather than mass for a slugfest with the Argentine fleet.

If the British fleet disperses, officials question whether Argentine planes can find them on the stormy seas. Both navies are handicapped for want of adequate reconnaissance planes.

As the news filtered into Washington about modern weapons destroying warships, some strategists contended anew that conventional surface ships cannot survive against "smart" weapons.

Former Defense Secretary Harold Brown recently told The Washington Post that of all the conventional warfare problems with which he had dealt, the most insoluble was how to protect surface ships from highly accurate cruise missiles.