Outside the heavily guarded headquarters where Argentina's military leaders are feuding for power waits an economically shattered and demoralized nation, burdened by decades of political and social maladies and pervaded by a sense of national failure in the Falkland Islands.

The new government that emerges from the latest rounds of Argentina's characteristically anarchic political bloodletting will probably end the prospect of further fighting with Britain in the South Atlantic. But it will be confronted by an economy that has all but ground to a halt in the last two months and divided political forces that, while no longer supporting military rule, have almost no viable alternative leaders or programs of their own.

While Argentina occupied the Falklands, both the government and much of the civilian leadership appeared to forget all but the cause of seizing the desolate, windswept islands. A popular theory developed that the crisis was somehow transforming Argentine society, curing it of its age-old divisions and its declining wealth, "maturing it at a single stroke."

Now, in the cold days after the surrender of Argentina's troops at Stanley, the costs of the nearly 11-week national adventure are beginning to be recognized for the first time. And the damage, intellectual and political leaders are saying, is appalling.

Argentine casualties in the weeks of fighting, say government and diplomatic sources, will shock the country if they are ever fully made known. Already, the military command has announced the evacuation of more than 500 wounded from the Falklands, and informed diplomatic sources say total Argentine casualties are believed to number 1,300 or more.

In addition, Argentina's military has lost hundreds of millions of dollars in equipment, including at least 30 percent of its warplanes and an arsenal of its most expensive missiles, artillery and other weapons, captured by the British on East Falkland Island. Although the government has now handed over millions of dollars in spare cash to arms dealers, diplomatic sources say new weapons have been slow to arrive and the armed forces remain badly weakened.

While the crisis has lasted, much of the government and the 60 percent of the economy it controls has been in a state of near suspension. Most large projects have been postponed and businessmen say almost all industrial orders have been held up. As a result, an already crippled economy is now rapidly collapsing.

Industrial activity fell sharply even during April, according to government figures released this week, and was down by 10.9 percent in the first third of this year compared to that period in 1981. Workers' real wages stand at 31 percent below last year, according to government studies.

Dozens of financial institutions have gone bankrupt in the past two months, and foreign reserves have been falling at the rate of $90 million a week. The Argentine peso has gone from about 11,000 to the dollar when the crisis began to as high as 25,000 now on the black market, and inflation remains at an annual rate of well over 100 percent.

Perhaps most significantly, the disastrous end of the Falklands conflict has badly weakened the Argentine armed forces as a political authority. Before the Falklands invasion April 2, the military government was already facing open opposition and violent demonstrations in major cities.

Now, following a humiliating surrender, the military can hope for little more than public passivity and political party acquiescence in an orderly, if hastened, retreat from power. Following the most severe outbreak of violent protest under this military rule Tuesday night, political analysts say, only brute force will now enable the armed forces to govern without a fixed departure date. The military is also unlikely to be able to pursue the conservative and restrictive economic and social policies it has long endorsed.

Many in the military leadership are said to be anxious to put an end to their fading government, abandoning altogether its plans for ending the economic and social chaos and political terrorism that dominated Argentina in the early 1970s.

The military's program, called the "process of national reorganization," was supposed to eliminate Argentina's leftist terrorists, reorganize its crisis-prone economy and rebuild parties to govern without the cycle of military coups and failed elections that has plagued Argentina since 1930.

In the most urgent areas, the economy and the political system, the military's grand project has failed. Argentina has continued to decline as an industrial power in the last six years. It continues to have the highest inflation rate in the world, and its foreign debt has risen from $9 billion in 1976 to an estimated $34 billion today.

The political parties, meanwhile, are even more fragmented and shapeless than before, and the military's plans for reorganizing them, once intended to establish large, stable parties with clear ideologies, have all but been abandoned in the past three months. Galtieri's government scrapped guideline after guideline from a still unfinished political law to win support from traditional party bosses.

Only the military's campaign against leftist terrorist groups is argued by government spokesmen to have been successful. But this "dirty war" was won at the cost of a violent campaign of kidnaping and assassination by paramilitary forces that has left military leaders with the responsibility of up to 15,000 "disappearances" in a population of 28 million.

Even at the height of patriotic support for the Falklands conflict, families of disappeared persons continued their weekly marches in front of the presidential palace. Now, a weakened military government, human-rights leaders say, will have difficulty escaping their demands for an accounting of the disappearances and deaths they are blamed for.

In most Latin American countries, the combined failure of the military's programs, the recent violent protests and the humiliating fiasco in the islands would quickly drive the generals from power. But the tragedy of Argentina, government and political leaders here say, is that decades of turmoil have left the armed forces--with all their weaknesses--as the only institution now capable of governing the country.

Even with the military's prestige at an all-time low, few major party leaders are calling for the immediate establishment of a democratic or even a purely civilian government. Instead, surrounded by the feuding remains of parties that have been inactive since the coup of 1976, they are proposing schemes that would lead to elections in no less than six months, believing it will take at least that long to establish programs and leadership.

The reality of the political situation, many leaders privately concede, may be more bleak than that. Not only do parties lack support or programs to address the country's problems, no strong new leadership has emerged within their ranks in more than 20 years.

The problems of political leadership outside of the military were capsulized recently when the Radical Party, the second most important political movement that traditionally has represented the moderate middle class, tried to reorganize in the prospect of the vacuum of military leadership.

According to the plan, the Radicals were to have proposed a government of "national salvation" to be headed by a Radical, Arturo Illia. But Illia has already served one failed presidency, during which he was known as the "tortoise" for his slow decision-making before he was overturned by a military coup in 1966. Now, Illia is 81 years old.

The country's most important political movement, Peronism, is no better off. Formed around the personalist leadership of three-time president Juan D. Peron, the movement split into a myriad of factions, ranging from the extreme right to the extreme left, even before Peron's death in 1974. Now, although a large percentage of Argentines describe themselves as Peronists, the party has no identifiable leader or ideology.

Many political leaders hoped the current turmoil would lead to a joint government of military and civilian leaders tha could build a consensus for Argentina's future. In exchange for a share of power and the adoption of the populist, government-managed economic policies favored by most political parties, the civilians would forgive the military their errors in fighting Britain and the human-rights abuses of the late 1970s.

But it is not clear that the emerging military leadership will be willing to accept collaboration with the Peronists, whose political battles with the military have been a constant theme since Peron was first overthrown in 1955.

"No matter who takes power, the situation will be unpredictable into the foreseeable future," said one former official of the military government. "No one has any answers for the situation the country is in now."