United Nations Secretary General Javier Perez de Cuellar said yesterday that Britain and Argentina had given a "positive reaction" to his proposals for resolving the Falkland Islands crisis, but officials in London and Buenos Aires said the two nations were still far from agreement.

For the second straight day, there was no combat reported in the South Atlantic, although Britain reported that two of its Sea Harrier jets were lost, possibly due to poor weather conditions in the wind-swept seas around the islands. Neither side ruled out further military action, however.

British Prime Minister Margaret Thatcher's Conservative Party won a strong vote of confidence for her government's handling of the Falklands crisis in local elections. Details on A26.

In a day marked by diplomatic maneuvering and aggressive public statements, each side said it was willing to use Perez's proposal for a cease-fire and mutual withdrawal of forces as "a framework for further talks," in Thatcher's words. But each accused the other of scuttling initiatives that would have brought an immediate halt to hostilities in the South Atlantic.

The main sticking points appeared to be Britain's insistence that any cease-fire be linked to an Argentine agreement to withdraw its estimated 9,000 troops from the Falklands, while Argentina insists that it must be guaranteed some form of sovereignty over the Falklands.

Thatcher told Parliament yesterday that without a guarantee of Argentine withdrawal, Buenos Aires could use a cease-fire to resupply and reinforce its garrison on the islands, which it seized April 2.

But Argentine Foreign Ministry officials said they will not negotiate any substantive points--including an Argentine troop withdrawal--until Britain agrees to halt military activities. "The situation looks like the same" as it was April 2, said one Foreign Ministry official.

Informed Argentine sources said Foreign Minister Nicanor Costa Mendez believed that the U.N. plan had potential, and the state news agency Telam reported that the vice minister of foreign affairs, Enrique Ros, left Buenos Aires last night for the United States. But the sources said that the ruling military junta had been far less interested in the U.N. proposal because it contains no guarantee of eventual Argentine sovereignty over the islands. The sources said junta members, for the moment, are taking a hard-line position and offering no concessions.

British Defense Secretary John Nott, appearing at a meeting of NATO defense ministers in Brussels, took a similarly pessimistic view at a press conference after the session. "My own belief is that there will not be a peaceful solution to this crisis unless Great Britain is prepared to keep up its military pressure . . . ."

Nott added, "We are dealing with a military junta. So far . . . there has been no evidence they understand anything but strength."

British Foreign Secretary Francis Pym, denouncing "Argentine intransigence," said Britain would have accepted a Peruvian cease-fire plan that the Buenos Aires government rejected over the weekend. He said the plan, which had the backing of the United States, would have led to a cease-fire at noon EDT today.

With the rejection of that plan, the U.N. initiative remained "the only negotiating mechanism in the field at the moment," said Anthony Parsons, Britain's ambassador to the United Nations.

While Parsons expressed "enormous confidence" in Perez and the proposal, diplomatic sources in Washington said neither Britain nor the United States placed much faith in the United Nations as a forum for working out a settlement. These sources said Britain's acceptance of

This article was compiled from reports by Washington Post correspondents Leonard Downie Jr. in London and Jackson Diehl in Buenos Aires, staff writer John M. Goshko in Washington and special correspondent Michael J. Berlin at the United Nations. the U.N. "framework" was dictated by Thatcher's need to protect herself against any charges by domestic opponents or European allies that Argentina had shown greater moderation and flexibility in seeking a peaceful solution.

The general expectation in Washington, the sources added, was that Argentina would use Perez's diplomatic effort as a delaying tactic and that any genuine movement toward a negotiated settlement will be put on hold until the Perez effort peters out. In the meantime, the sources warned, there is heightened dangerof new fighting.

Publicly, U.S. officials refused comment except for brief remarks made by President Reagan to reporters at the White House. The president reiterated the U.S. view that a settlement must be within the framework of U.N. Security Council Resolution 502--a cease-fire coupled with an Argentine withdrawal.

Reagan refused to single out a particular approach as the best road to a solution. "We're open to every approach," he said.

The Perez plan proposes a cease-fire followed by a simultaneous Argentine military withdrawal and pullback of the British naval task force that has conducted military operations in the South Atlantic for the last two weeks. It suggests that the United Nations provide or oversee an interim administration of the islands while negotiations take place to decide their future. It also proposes that specific dates be set for the talks to begin and for their conclusion.

But the question of sovereignty--which was the major stumbling block in the unsuccessful diplomatic effort conducted last month by U.S. Secretary of State Alexander M. Haig Jr.--is left unresolved.

U.N. officials said that before deciding how to proceed, Perez and his Falklands task force would first study the replies from Britain and Argentina, seeking out possible areas of common ground. "I hope to act at an accelerated pace with the hope of achieving positive results in a matter of hours or days," Perez told reporters.

The British reply was delivered yesterday afternoon by Ambassador Parsons, who said it "is substantial and constructive and addresses all aspects of the secretary general's ideas."

By contrast, the Argentine response delivered Wednesday night was said to be far less specific, although it urged an immediate cease-fire and--like the British--accepted the secretary general's plan as the basis for further negotiation.

Perez said he had asked Argentine Ambassador Eduardo Roca for a more detailed reply and was told one would be forthcoming.

Foreign Ministry officials in Buenos Aires said Argentina may respond within a couple of days to Perez's specific ideas. But there seemed to be little movement by Argentine officials toward advancing the U.N. mediation. Foreign Minister Costa Mendez, who had been reported to be planning to discuss Perez's plan with him personally, continued to postpone any visit to New York because no formal meeting of the U.N. Security Council had been scheduled.

Asked if the British fleet would be pulled back provided Argentine troops do the same, British Ambassador Parsons replied:

"If Argentina agrees to withdraw without attaching unacceptable conditions, I have no doubt that a simultaneous withdrawal of the British and Argentine forces could take place. But Argentina must first give an unequivocal commitment."

One British problem, referred to by Thatcher in announcing to Parliament her response to the U.N. plan, is the need to be sure that both the withdrawal and the temporary U.N. administration are "effectively applied, maintained and guaranteed," as a British diplomat put it.

"We are not worried about the U.N.'s ability to do this," he went on, "but we must make sure the U.N. could not be kicked out by a new bunch in Buenos Aires."

The British apparently feel the need for a peace-keeping force of some sort to oversee the staged withdrawal of forces.

Other diplomats say the unspoken British reason for preferring a non-U.N. mediation effort is that a majority in both the Security Council and the General Assembly are certain to back Argentina in its demand for ultimate sovereignty.

While Britain can block the council with a veto, and assembly resolutions are not binding in this situation, the British are said to feel that these pressures could influence the negotiating process against them.

Argentina and Britain have each accused the other of attempting to manipulate the United Nations to seek advantage over the other. Argentine officials have accused Britain of blocking a Security Council meeting requested by Ireland so that it will not have to vote on any initiative that calls for an immediate cease-fire without a troop withdrawal.

In Parliament yesterday Thatcher said "it may be very likely" that Argentina was using the United Nations to gain a cease-fire without being forced to withdraw militarily. "That would be a very evident ploy to keep them in possession of their ill-gotten gains, and we are right to be very wary of it," she said.

This week's sinking of the Argentine warship General Belgrano and the crippling of the British destroyer Sheffield has increased pressure on both sides for a settlement. But like the junta, Thatcher's government is also under domestic pressure from hard-liners not to agree to any negotiated settlement that does not meet British conditions. These conditions include a complete Argentine withdrawal from the islands, restoration of British administration and a guarantee of self-determination for the islands' 1,800 inhabitants, most of whom prefer to remain part of Britain.

More than 20 members of Thatcher's Conservative Party yesterday introduced a House of Commons motion urging immediate recapture of the islands using whatever "measures should prove necessary," including the bombing of air bases on the Argentine mainland.