Argentina's military junta, confident that it has the advantage diplomatically and militarily in its conflict with Britain, has spurned suggested solutions to the Falklands crisis in the belief that time will only strengthen its hand, according to governmental and political sources.

The junta has taken this hard-line position even though it has suffered losses significantly beyond those that have been publicly revealed, a source close to the military command said, and in the belief that far more damage was inflicted on the British fleet than has been admitted by London.

In brief, the generals and admirals running the country are pictured as believing that Argentina remains in a superior position militarily and can inflict even greater losses on Britain's fleet.

Underscoring this view was Argentina's apparently deliberate slow motion on the diplomatic front, even though civilian political leaders and some Foreign Ministry officials have said the peace plan offered by U.N. Secretary General Javier Perez de Cuellar is potentially workable.

While the undersecretary of foreign relations, Enrique Ros, traveled to New York today to talk with Perez de Cuellar, Foreign Ministry officials characterized the mission as only for "preliminary negotiations."

"The Perez de Cuellar plan is a good plan," said one well-informed source here. "But at least until yesterday , the military has been very tough. They are tied up in their words, in what they have said about sovereignty. They feel victorious. They are military men, and they seem inflated with success.

"When the British make a landing and establish a beachhead on the Falklands, then the military will talk," this source predicted. "Until then, it will be hard for them to make real concessions."

Sources here said the military, judging itself to be in a strong position, believes the U.N. negotiating process may simply be a way to buy time for both countries.

Many in the military leadership are said to hold that Britain is waiting for reinforcements to arrive in the South Atlantic before launching another major attack on Argentine forces in the Falklands.

The Argentines are using the lull in the fighting to reinforce and prepare their own forces for what they believe could be a decisive battle, these sources said. Among other measures, one source close to the military command said, Argentina is seeking new military equipment, such as rockets, from its allies in Latin America.

The military's tough stance on the diplomatic front is attributed by sources here to the overall assessment by the generals of the line of battle so far--which they apparently believe is positive, on balance, despite setbacks.

In its formal communiques during the past week, the military command has conceded a total of 28 dead and 37 wounded on the Falklands and on the tug Sobral, which was said to have been badly damaged. No estimates of killed and wounded have been formally made on the sinking of the cruiser General Belgrano, which was torpedoed by a British nuclear submarine Sunday.

In communiques, only two Israeli-built Daggers and an Argentine-built Pucara have been reported lost. But Argentina's losses, according to one source informed by high military officials, have been greater than that.

The source said that the military estimates a loss of at least 200 of the 1,042 crew members of the General Belgrano. In addition, the source said, Argentina has lost a number of aircraft--including Canberra bombers, helicopters, and one of its French-made Super Etendard fighter bombers--that have yet to be acknowledged.

The main airstrip on the Falklands outside Stanley can still receive cargo from Argentina's C130 aircraft, this source maintained. But the strip has been badly damaged by British bombing, and though repaired with aluminum sheeting, is now "somewhat shorter" than its original length, the source said.

Military officials no longer consider the Falklands airstrips as suitable for Argentina's sophisticated warplanes. As a result, Argentina is impeded from launching a strong air attack on the British fleet by the necessity of basing aircraft on the coast, at least 400 miles from the Falklands, the source said.

The commanding Argentine Army general in the southern coastal area, Osvaldo Garcia, told Argentine journalists in the area today that the "air bridge" of supplies between southern Argentine port cities and the Falklands had been temporarily stopped, according to a report in the evening newspaper, La Razon. Garcia was quoted as saying that the flights ofcargo planes carrying supplies to the island were halted at times because of the possibility of a British attack, but that the supply route remained open when needed.

The difficulties were demonstrated during fighting on Saturday when one of the Super Etendards ran out of fuel after an attack on the British fleet and, unable to be refueled in the air, crashed into the ocean, according to the informed source.

This account of Argentine military losses could not be officially confirmed. In the past week Argentine military officials have given numerous versions of their own and British losses while at the same time publicly declaring that they were waging a "psychological war" with the English.

While these losses have weakened Argentina's military strength, the high command appears to be convinced that Britain's military position is worse, according to sources close to the military.

Military officials here apparently believe the British have lost more than the three Sea Harrier fighters it has admitted. Formally, Argentine military officials have said that at least nine Sea Harriers have been shot down. Naval officials, according to sources, are persuaded that ships other than the demolished destroyer Sheffield may have been significantly damaged by Argentine attacks.

At the same time, another source said there is uncertainty within the military as to the precise results of some attacks. As an example, the source said, the Argentine planes that attacked the British fleet on Tuesday fired from long range at what appeared to pilots only as radar signals on their screens, then quickly turned back to their bases.

British officials subsequently announced the Sheffield had been destroyed. But military officials believe that another craft could have been damaged, and that attacks on the British fleet on Saturday may have caused damage that Britain has not admitted, according to informed sources.

"They the military feel they're at least at a draw with the British, and that is something when you're fighting a power like England," said one Argentine source here.

As for the renewed diplomatic activity at the United Nations, "if the results are positive for Argentina," one official said, then the U.N. peace initiative might be taken up in a trip by foreign minister Nicanor Costa Mendez to the United States.

Costa Mendez's visit to New York has been consistently linked here to a formal meeting of the U.N. Security Council. Officials here indicated today that such a meeting would probably not be called unless Perez de Cuellar's private talks with Ros and British officials brought the two sides close enough that the Security Council could formally discuss a settlement.

Costa Mendez said in a radio interview today that there was "definite hope" for an accord with Britain and that "at this time we are trying to give a diplomatic response, in order to achieve a peace that is honorable and just."

But other Foreign Ministry officials and sources close to the military command described a more pessimistic outlook. At the same time, the military command is said to believe support for Britain's tough position on a settlement, both internally and among its allies in Europe and the United States, is weakening.

In contrast, there has been no discernible opposition to Argentina's military initiatives within the country, and officials say support for Argentina is increasing among its Latin American neighbors.

Thus the junta, while willing to pursue the U.N. mediation effort and hold off on any military offensive of its own, is not disposed to weaken Argentina's claim of sovereignty over the South Atlantic islands in return for a settlement, Argentine political sources say.

The difficulty in the Perez de Cuellar plan for the junta, sources said, was a variant of the same problem that has impeded negotiations from the beginning. While offering fixed dates for negotiations over the islands' future, the plan avoids the issue of sovereignty entirely, according to sources here.