The collapse of Venezuela's largest bank has exposed a history of political mismanagement and corruption here that has tainted the two dominant political parties and turned this year's presidential election into an ugly debate over the abuse of money and power.

The still unfolding scandal began Nov. 29 when the government took over operations of the Venezuelan Workers' Bank, a specially created mortgage and commercial operation that had been controlled by the labor movement in partnership with the central government. The government move dealt a resounding shock to Venezuela's already troubled business and political establishment.

About 400,000 depositors found their accounts threatened, and construction of up to 15,000 housing units funded by the bank reportedly was frozen, leaving thousands unemployed.

Now, as bank auditors, government-appointed managers and a congressional commission have sought to determine how the bank became insolvent, a massive and complex pattern of mismanagement has emerged involving the national labor confederation, the opposition Allied Social Democratic Party (known as Democratic Action) and the government.

Even in Latin America's richest country, accustomed for a decade to bounteous and loose petrodollars, the scale of the irregularities appears immense.

Banking authorities have reported that up to $2 billion in loans by the bank may have to be written off as losses--including at least $1.7 billion in often unsecured loans to companies owned and created by the bank and its governing labor confederation.

While the activities of many of the companies and the use of the money remain unclear, the political importance of the figures involved is unquestioned. Among the directors listed in many of the companies is Jose Vargas, the president of the Venezuelan Confederation of Labor and vice president of Democratic Action.

A constellation of other union and opposition party figures has been tied to the operations by official audits and public documents, including Democratic Action's secretary general and the personal secretary of the party's candidate in this December's presidential election.

While the government of President Luis Herrera Campins--who heads the Christian Democratic party known as COPEI--has been accused of launching the scandal in an effort to cut Democratic Action's long lead in campaign polls, leading government figures also have been touched by the revelations. The comptroller general reported that current government officials covered spending shortfalls by overdrawing accounts at the bank by at least $183 million, an apparent violation of laws to control banking and government debt.

COPEI officials, who helped the bank to more than triple its assets in less than four years, also are accused of ignoring or even covering up the bank's irregularities before its collapse.

"This is a scandal that could bring everyone down," declared Jorge Olivarria, a presidential candidate for a small leftist party whose widely circulated magazine has published much of the documentation in the case. "Nothing like this has ever happened, on this scale, in the financial history of the world."

Such hyperbole has become rampant in Venezuela's public forums as each of the two leading parties has sought to shift the specter of corruption to the other. Emboldened by the airing of irregularities established by bank audits, politicians and labor leaders have begun to accuse each other of alleged crimes for which no evidence has been offered.

As the charges have mounted, many leaders say they have become concerned that the scandal will leave both major parties publicly discredited in an election year. The result, they say, would be the destabilization of Venezuela's 25-year-old democracy, for many years the most respected in Latin America.

"Democracy is passing through a critical moment in Venezuela," said Luis Pinerua Ordaz, a one-time Democratic Action presidential candidate and one of a handful of political leaders who have pressed for a full criminal investigation of the corruption charges. "What has happened is truly grave because not only had the saving of hundreds of thousands of people been put in jeopardy, but also their faith in the democratic system and legal processes."

While few analysts here are predicting the demise of Venezuela's stable political institutions, the history of the Workers' Bank has shown how the two established parties were drawn into a corrupting netherworld of financial high rolling and political patronage by the oil revenues that flooded Venezuela with sudden wealth in the 1970s.

The bank, created by a special government act in 1966 by a Democratic Action administration, was one of the most ambitious social projects launched during the country's years of growth. With a controlling interest held by the Democratic Action-controlled Venezuelan Confederation of Labor, the bank was meant to be the financing source for a wide range of social projects and worker-managed enterprises.

Even after Democratic Action lost power and Herrera Campins was inaugurated in 1979, the growth of the bank took off. Helped by huge government deposits and interest rates as much as two points higher than other banks', the Workers' Bank boomed from $1.6 billion in assets in 1979 to $5.8 billion last year.

But even as the new money poured in, bank directors, union leaders and government officials began to drain hundreds of millions of dollars in irregular loans, questionable long-term investments and overdrafts.

The bank's president, former labor leader Eleazor Pinto, served as president of 46 firms that received hundreds of millions of dollars in loans without guarantee, including $230 million in credits that Pinto personally granted to his firms on one single day just before the bank was taken over by the government, according to audit reports. Pinto has denied any wrongdoing.

Other questionable loans were made to companies involving union leaders and figures from both major parties. Meanwhile, government officials drained other reserves from the bank through unauthorized overdrafts.

While many of the companies set up by bank, labor and party officials were involved in housing or other social projects, others appear in bank documents to have done nothing more than borrow huge sums of money before becoming insolvent.

As Venezuela's money supply shrank with a dropoff in oil revenues, it became more difficult for the bank--with the uncollected loans--to cover its obligations.

As the irregularities mounted, government banking authorities asked that the government take over the operations at the bank as early as February 1981. Government officials delayed action while continuing to pump up the bank's assets, apparently out of reluctance to take on the powerful political interests involved.

Banking officials say the government may now have to appropriate as much as $1.6 billion for the bank to cover obligations, and even then the institution may have to be liquidated so that depositors can regain most of their money.

Meanwhile, it is still unclear what action will be taken against the officials in both parties and the labor union apparently involved in irregularities. The extent of the abuses--and the implications for both established parties--are such that many analysts suggest little will be done.

Yet a long campaign season lies ahead, even as auditors continue to probe the bank's files. "All the politicians are publicly saying that this should be taken to its final consequences," said Olivarria. "But they don't realize themselves how serious the final consequences" may be.