Six months before Argentina's planned return to democratic elections, the white tower of the General Confederation of Labor still stands vacant here behind steel-helmeted guards.

But each time the nation's union leaders gather in their backstreet apartments and dusty converted warehouses, they seem a step closer to controlling a decisive year of electoral politics.

Their strike funds and car fleets remain commandeered by military administrators, and their bureaucracy is split into two snarling fronts. Since December, however, labor unions have led two successful national strikes, outmaneuvered political parties and opened bargaining with military leaders about the future constitutional government.

For a handful of top labor chiefs, history, style and a touch of conspiracy have all but overcome seven years of military government efforts to break their political clout. And for many Argentine politicians, these tough, blunt-spoken men have become the most potentially disruptive element in the fragile reconstruction of democracy.

"This is not a democratic process," complained one leader of the centrist Radical Party. "It is a clique of labor leaders standing between the armed forces and the politicians, manipulating and looking for deals. Today they are democrats because it suits them. Tomorrow they could pact with the military."

With their strikes and new plans for mobilization, the unions have effectively replaced political parties as the popular leaders of widespread antimilitary sentiment, and shaken the stability of Gen. Reynaldo Bignone's moderate transition government.

At the same time, the quiet bargaining with military officers has prompted a rash of bold headlines in Argentine newspapers about a possible labor-military "pact" that could determine the next constitutional government.

"What is happening is that we are confronting the political realities, the political explosion, while the parties work on 1984," said Armando Cavalieri, a leader of the 100,000-member Commercial Workers. "We are the ones closest to the fire."

The men behind these intricate dealings are also all too likely to offend the middle class sensibilities of Argentina's moderate politicians.

Mostly raised in Buenos Aires' industrial suburbs and empowered in the three postwar governments of Juan Domingo Peron, the chiefs of the nation's 1,000 unions have rarely varied from the enduring doctrine of Peronism--or its founder's autocratic style.

It was Peron who made Argentina's unions into the most powerful and politicized labor movement in Latin America by constructing a single national leadership in the General Confederation of Labor and incorporating it as an arm of the Peronist party.

Now, with Peronism once again favored to win control of the government, this peculiarly Argentine brand of leadership is embodied by men like Lorenzo Miguel, a silver-haired metal worker who for a decade has been the single most powerful Peronist labor chief.

Explaining why he believes former president Isabel Peron, Juan Peron's widow, should be named head of the Peronist party, Miguel recently told the magazine Somos that " Juan Peron wanted it that way, he put her there, and what was good for Peron is good for me."

Ironically, it has been the deep divisions among the national labor leaders that has helped propel them back into the center of politics.

Both Peronist politicians and their counterparts in the labor movement are split into two broad camps, in part by personal differences and in part by conflicts over the future of the Peronist movement.

These political disputes are reflected in the current division of labor--almost all of which remains Peronist controlled--into two separate national organizations, both calling themselves the General Confederation of Labor.

But the dynamics of the union battle are even more intricate. Above all, national union leaders are concerned with the control of Argentina's big industrial unions and their large financial holdings, and most of these remain in the power of the military government.

The resources at stake are more than enough to swing both Peronism's choice of a presidential candidate and the subsequent national election. Aside from a membership of about 3.5 million, Argentina's unions have historically controlled national health and welfare systems, including dozens of hospitals and hotels, and their combined economic empires have been estimated as equal to 4 percent of the country's gross national product.

Military officials once vowed that these resources would remain in the hands of the government, and that national labor organizations would be banned. But as military leaders have looked for ways to restore their political position and influence in the planned civilian government, the lure of the divided unions seems to have become increasingly attractive.

"The Army thinks the Peronists will win the elections, and it wants to ensure that with the new government its leadership remains in power," said a former military government official. "So it is trying to establish its position by dealing with one of the labor groups."

The results have been an intricate minuet of maneuvers by various military sectors and the two labor organizations, and the transformation of Peronism's internal battle into a national political issue.

Military authorities have the power to swing the allegiance of many government-administered unions by appointing "normalizing commissions," which theoretically organize internal union elections but which in practice can all but determine which national labor confederation wins control of the union.

Government officials also say they now are studying the possible return to the unions of the social welfare system. In return, say labor and political sources, the armed forces will expect the winning confederation to influence favorably the Peronist party on the issues most important to the military, such as the new government's approach to human rights violations by the armed forces.

Now, as both the military "normalization" of the biggest unions and the Peronist party congress approach, both confederations have threatened new "measures of force" to establish themselves as the dominant group and force the government's hand.

"It may seem contradictory," said one top leader who asked not to be named. "But what it all comes down to is a simple battle for power." national union leaders are concerned with the control of Argentina's big industrial unions and their large financial holdings, and most of these remain in the power of the military government.

The resources at stake are more than enough to swing both Peronism's choice of a presidential candidate and the subsequent national election. Aside from a membership of about 3.5 million, Argentina's unions have historically controlled national health and welfare systems, including dozens of hospitals and hotels, and their combined economic empires have been estimated as equal to 4 percent of the country's gross national product.

Military officials once vowed that these resources would remain in the hands of the government, and that national labor organizations would be banned. But as military leaders have looked for ways to restore their political position and influence in the planned civilian government, the lure of the divided unions seems to have become increasingly attractive.

"The Army thinks the Peronists will win the elections, and it wants to ensure that with the new government its leadership remains in power," said a former military government official. "So it is trying to establish its position by dealing with one of the labor groups."

The results have been an intricate minuet of maneuvers by various military sectors and the two labor organizations, and the transformation of Peronism's internal battle into a national political issue.

Military authorities have the power to swing the allegiance of many government-administered unions by appointing "normalizing commissions," which theoretically organize internal union elections but which in practice can all but determine which national labor confederation wins control of the union.

Government officials also say they now are studying the possible return to the unions of the social welfare system. In return, say labor and political sources, the armed forces will expect the winning confederation to influence favorably the Peronist party on the issues most important to the military, such as the new government's approach to human rights violations by the armed forces.

Now, as both the military "normalization" of the biggest unions and the Peronist party congress approach, both confederations have threatened new "measures of force" to establish themselves as the dominant group and force the government's hand.

"It may seem contradictory," said one top leader who asked not to be named. "But what it all comes down to is a simple battle for power."