rgentina's military government, while maintaining a firm outward stance in its confrontation with Britain over the Falkland Islands, has moved to use the fervent nationalism stirred by the crisis to try to win a decisive internal victory over its once-formidable political adversaries.

Even as they sketch the delicate diplomatic formulas seen here as the basis for international negotiations over the islands, high-ranking government officials reportedly have been equally preoccupied with the domestic political realignment that will almost certainly follow the crisis.

Confident that Argentina will emerge from the conflict with the archipelago it has long coveted, the military command appears to hope that what had been a failing effort to transform the six-year-old armed forces administration into some kind of permanent national political force will succeed quickly.

While slowly planning the military's retirement from the government this year, President Leopoldo Galtieri has sought to win a popular base of support that the military hopes eventually will emerge as the country's dominant movement in a restored democracy.

Until now, these efforts had been ridiculed by Argentina's traditional civilian political and labor movements. By late last month, these movements had mounted a broad front opposing military rule and increasingly had appeared to threaten the government's stability.

But the balance of political forces, party leaders admit, has been suddenly upended by the armed invasion of the barren, seemingly valueless island territory. The islands have been a symbol of nationalistic sentiment here since the rule of populist president Juan D. Peron.

The international crisis prompted the opposition to drop its open campaign against the government in favor of a united domestic front against the British. Beneath this outward solidarity, military and political leaders have tried to gain through quiet maneuvering what they sought in open confrontation a month ago.

With military leaders firmly in command of the island's defense and Argentina's negotiating tactics, Galtieri's government has been able to take charge of popular leadership. It has also upstaged the fierce independence of the military's traditional labor and Peronist political adversaries.

As Galtieri strode onto the pink, stone balcony of the presidential palace here Saturday to address a sea of cheering Argentines, the military seemed to have achieved at least temporarily much of what it sought when it actively launched its political "normalization" process three months ago.

Although the crowd had been drawn by patriotism in the face of an international threat and chants of the Peronist party greeted Galtieri's appearance, thousands also chanted Galtieri's name and screamed their approval as he shook his fist at the English threat and flashed a victory sign in the manner of Winston Churchill.

Meanwhile, opposition labor leaders in charge of major antigovernment demonstrations in recent days have been pictured prominently riding government planes to ceremonies on the disputed islands and standing in crowds cheering Galtieri.

For the military, this commanding political position appeared to be just as important as the talks under way with U.S. Secretary of State Alexander M. Haig Jr.

Borrowing Peron's tactics, government officials offered free transportation Saturday to all who gathered in the plaza facing the presidential palace. Galtieri also seemed to downgrade his delicate talks with Haig by appearing to deliver a rousing, crowd-oriented speech only moments after Haig departed by helicopter.

The encouragement of the demonstration and Galtieri's populist gestures were unprecedented during the long years of military government. They took on particular significance in view of the government's continuing pledge to allow reorganization of political parties within the next several months.

Since January, government officials have been hinting that there was a need for an organized political movement on the moderate right to challenge the Peronists, whom the military has been seeking to eliminate since 1955.

Galtieri denies that he intends to create a political party "by decree." Yet he has been seen widely by political observers as seeking to build a personal following that could be used by him or by a military-allied civilian in future elections. Popular support for Galtieri's government could also be used by the military to justify the naming of another military president when Galtieri's term ends in 1984, according to political analysts here.

In recent days, opposition political leaders have sought to check the government's political momentum by establishing themselves as public leaders on a par with the military in defending the taking of the islands.

Opposition parties' leaders here obtained an audience with a State Department official accompanying Haig and publicly released a document asserting Argentina's sovereignty during the U.S. delegation's visit. Now, leaders of the country's opposition labor unions and several political parties are planning trips abroad to argue Argentina's position while trying to gain internal recognition as a diplomatic force.

But these measures, political leaders say, cannot reverse the dominant political position of the government while the Falkland dispute continues. If Argentina emerges from the dispute with its flag still flying over the islands, they say, Galtieri may have ensured himself a place in power for several more years.