Buenos Aires — While Washington pursues its frantic search for a formula to avert South Atlantic war between Argentina and Britain, the probability of such a war looms ever larger here.
The Argentine military doubts that conflict with the British can be averted. Military officials are understood to feel that war is likely to break out within 48 hours. At time of writing Thursday, the Argentine military forces were on full battle alert.
Foreign Minister Nicanor Costa Mendez has stayed in the United States conferring in both Washington and New York in his own last-minute quest for a way out of the escalating crisis. And it was still thought possible here Thursday that US Secretary of State Alexander M. Haig Jr. might shuttle down to Buenos Aires this weekend.
But Argentine government sources have virtually given up hope of success for his mission. They say the military government rejects the latest Reagan administration plan to defuse the crisis. They add that the plan is little different from others that Mr. Haig tried out on Argentina during his two diplomatic missions to Buenos Aires earlier this month.
''Time has run out,'' says an official in the Casa Rosada (Pink House), the Argentine White House. ''The negotiations are a dead issue.''
The details of the latest Reagan plan are not clear. But from here it is understood to be much like earlier US proposals, calling for a sharply increased US role in a tripartite Argentine-British-US rule of the Falklands, including a heavy US troop presence. But the proposal has apparently run into difficulties here because it does not include guarantees for Argentine sovereignty over the islands.
Nonetheless, a thin thread of hope that mediation may eventually yield results prompts the US to keep trying. Hence the Haig offer to visit Argentina again. And, it is noted here, not only is Mr. Costa Mendez still in the US and talking with Mr. Haig, but also the Argentines have not told the US secretary of state to stay away from Buenos Aires.
An Argentine newsman in Washington, asking a key Latin American diplomat what comes after the current talks between Mr. Haig and Mr. Costa Mendez, was told:
Yet opportunities for a peaceful solution to the crisis are dimming by the hour. The Argentine military under President Leopoldo Fortunato Galtieri is reconciled to fighting the British even though they privately admit the prospect scares them. The Argentine military has not fought a war in this century.
The Argentine fleet, hovering in the ports of Bahia Blanca and Ushuaia for the past two weeks, sailed Wednesday ''prepared to do battle'' with the British armada now hovering in waters adjacent to the Falkland Islands.
That British task force was ready Thursday to put into effect a total air and naval blockade of the Falklands, warning the Argentines that the island's capital of Port Stanley (renamed by the Argentines Puerto Argentino) may be attacked. The blockade, which covers a radius of 200 miles around the Falklands, was scheduled to take effect at 7 a.m. today.
An Argentine ship was reported to have run the earlier-established sea blockade of the islands and arrived in Port Stanley late Wednesday. But air flights between the Argentine mainland and the islands were suspended due to turbulent weather now beginning to ravage the South Atlantic with winter's approach.
Whether the Argentines will try to run the British blockade-- either in the air or on the sea--and whether the Argentine fleet will take on the admittedly superior British fleet remains to be seen.
Argentine military officials are naturally keeping all their options open. They feel that their country's biggest asset in the brewing war with Britain is clearly geography.
If war does break out in the stormy South Atlantic waters, the Argentines have the advantage of fighting close to home in familiar territory and with short supply lines.
In contrast, the British fleet's home base is halfway round the globe, separated by more miles than separate New York from Tokyo.
The Argentines are not advertising the strategy they intend to use against the British. But Argentine military spokesmen, although a bit jittery about the subject, feel that the Argentines will be able to hold their own.
For the moment, the Argentine fleet is at sea ''somewhere in the South Atlantic.'' Army units in the Falklands, with at least 10,000 men, are reported on ''maximum alert'' against the British landing--a landing that is already rumored to be under way on West Falkland by elements of the Royal Marines.
And the main elements of the Argentine Air Force were gathered at half a dozen air bases along Argentina's southern Patagonia coast, including Bahia Blanca, Comodoro Rivadavia, Rio Gallegos, and Trelew. A squadron of interceptor jets was said to be based at Port Stanley, whose airport has a newly lengthened runway.
Argentine strategy seems to revolve on presumed superiority in the air and on land.
Argentines think the British will have a problem enforcing the blockade. If the two British aircraft carriers move close to the Falklands, the ships would be within range of land-based Argentine interceptor craft.
Unless the British could take out the air bases, or knock down the Argentine warplanes themselves, British landing parties on the Falklands could be at the mercy of Argentine air superiority. The windswept and treeless islands have only sparse ground cover.
The British, it is recognized here, have obviously taken all this into consideration. But the Argentines return again and again to what they regard as their biggest asset--geography. Fighters, ships, and troopers are all close to their supply bases on the mainland.
There is growing awareness that any conflict could get caught up in some of the worst winter weather anywhere in the world.
The waters around the Falklands are cold, foggy, and subject to sudden violent storms. The nearest Argentine shelter is 350 miles west at Comodoro Rivadavia, also subject to violent winter winds. The nearest possible British shelter is 800 miles southeast in the South Georgia Islands.
Meanwhile Argentine military planners debate whether the British Royal Marines would be a match for the Argentine land forces. The military here is clearly jittery about the prospect that the British may already have come ashore on the Falklands.
They also worry that the Argentine military forces on the Falklands may be no better prepared for the rough weather than the British, although they are more heavily equipped. Argentine military leaders realize their soldiers are mostly teen-age conscripts. The majority of them apparently come from the warm northern provinces of Argentina and are unaccustomed to both the frigid climate and inhospitable terrain of the Falklands.