How much longer Latin America's major debtors will be willing to pay tens of billions of dollars a year to western governments and banks is the major question today in the Latin American debt crisis.

During most of the 3 1/2 years since Mexico ran out of money and touched off the crisis, analysts worried not about their willingness, but about their ability to pay.

Debtors are growing restive. Interest rates remain high and the debtors are finding it increasingly difficult to earn the export revenue they need to pay their foreign bills, buy vital exports and invest in their economies.

So far, no important debtor has made serious noise about repudiating its foreign debt obligations.

But the major debtors -- Brazil, Mexico, Argentina, Venezuela and Chile -- have bought their improved ability to pay their foreign debts at great cost since the start of the crisis in 1982. All experienced severe recessions. Unemployment soared and remains high. There has been a massive reduction in the standard of living for all but the wealthiest of Latin American citizens.

Even though most countries are not repaying any of the $360 billion of outstanding principal, confining their debt service to interest payments, the payments are a major drain on their economies.

Brazilian Foreign Minister Olavo Setubal warned in a recent interview that debtor nations can stand the severely reduced standards of living for only so long without seeing light at the end of the tunnel of austerity.

Peru's new populist president, Alan Garcia, already has announced that the country will pay no more than 10 percent of its export earnings to service its debts. That's about $300 million a year, far less than its annual interest bill of $1 billion to $1.5 billion. Not only has Peru refused to pay most of its bank interest, it has even cut off the International Monetary Fund.

Nigeria, one of the larger debtor countries outside Latin America, has said it would like to keep its debt payments to about 30 percent of its export earnings. But Nigeria's oil revenue is still high enough that it would be able to pay its interest and some of its principal with the restriction.

Peru's action was accompanied by an austerity program -- although one not approved by the IMF. However, other debtors have rejected Peru's approach. "Peru seems convinced that it can get by without the international financial system for a while. No one else has made that judgment," according to one Latin American finance minister.

But how much longer political and social forces in the debtor nations will endure austerity without the promise of renewed economic growth is a serious question, according to analysts and Latin American officials themselves. For most countries, the situation is not as dire as it was two years ago, but improvement has been limited. Commodity prices and world trade remain depressed. Interest rates, although lower, are still high in relation to inflation.

Not only does debt evoke austerity concerns, but it also reeks of foreign controls over debtor nations, and is an easy issue to play especially in the highly charged nationalistic politics of Latin America -- which in the last two years has added democracies in Brazil, Argentina and Uruguay.

"In country after country, the notion of debt relief is called for not only by extremes, but by people in the heart of the political establishment," said Sally Shelton-Colby, a political and economic analyst for Bankers Trust Co.

Brazilian President Jose Sarney has temporarily defused the debt issue by refusing to deal with the IMF, the multinational agency whose seal of approval generally has been required by banks as a prerequisite to renegotiating loans. The IMF, which many Latins believe tries to impose austerity on debtors, touches off even more raw nationalistic nerves than does the debt itself.

Unlike Peru, Brazil still talks to the IMF and is willing to explain its economic programs. Banks and Brazil are negotiating this weekend about whether the banks will push off repayment of about $16 billion in principal payments even though Brazil has no IMF program.

Argentina was once the most contentious of the debtor nations. But President Raul Alfonsin defused both the IMF and the debt issue last June. He convinced his nation that hyper-inflation (price increases were at an annual rate of 1,300 percent then) was Argentina's most serious problem and that until the country changed its economic policies, it could not expect foreign governments and banks to give it relief.

Alfonsin imposed a wage and price freeze and a series of other measures to slow inflation. The Argentine economy plunged into a recession, but Alfonsin's political standing skyrocketed in inverse relation to inflation.

But Alfonsin's experts still have not figured out a way to remove the freeze, and serious flooding last year may hit hard at the country's grain harvest -- its most important source of export earnings.

During the last half of 1984 and the first half of 1985, Mexico seemed to show that there was a light that Brazil's Setubal is searching for at the end of the tunnel.

The country that touched off the debt crisis also rapidly and thoroughly embraced the types of austerity measures western governments, through the IMF, said were necessary before countries could get back to normal.

Mexico, the model debtor, had reduced inflation, built up its depleted reserves of vital foreign currencies, cut back its budget deficit and was current on all its interest obligations to foreigners. The banks rewarded Mexico by stretching out for 14 years the repayment of its outstanding debts. After a wrenching recession in 1983 and early 1984, Mexico had resumed growing.

Today, Mexico is back in the soup. Starting in 1984, the government allowed its economy to grow too fast and, because of elections last year, took no steps to slow it until August. By then, inflation accelerated and imports had grown too fast. Exports declined as Mexican businessmen could sell at home again. Investors once more lost confidence in the government and began to secrete vitally needed dollars out of the country.

Although its problems are not as severe as they were in 1982, the country is returning to the IMF and austerity -- with all its attendant social costs and risks.

"They screwed themselves, for the most part," said a top international official at a major New York bank. "But that's a hindsight judgment. Nobody thought they were making a big mistake [when they began to stimulate the economy]. Not the Mexicans, not the banks nor anybody else."

To compound Mexico's problems, the price of oil has begun to decline, and the decline may accelerate if a price war breaks out among petroleum producers. Oil accounts for 70 percent of Mexico's export revenue and 45 percent of its taxes.

It apparently was the deterioration in Mexico's fortunes that convinced the Reagan administration that it had to find a way to pump more money into Latin America -- to enable the countries to pay their debts without resorting to the destabilizing austerity of 1982 and 1983.

U.S. Treasury Secretary James A. Baker III annnounced the government's new program in early October. He called on banks to boost their lending to debtor nations from virtually nothing in 1985 to about $7 billion a year for the next three years. Multinational development institutions like the World Bank and the Inter-American Development Bank are supposed to kick in another $20 billion -- $9 billion more than they had anticipated lending.

In return, Baker said debtor countries should change their economic policies to encourage economic growth and investment. Although Baker's plan was purposefully vague, the measures he advocated include removing barriers to foreign investment, selling off inefficient state enterprises and reducing bureaucracy and regulations that hinder private enterprise.

"The Baker plan is a change in tactics, not a change in strategy," according to William Cline, an international debt expert who is affiliated with the Institute for International Economics.

The plan does not involve any debt relief for the countries. Nor does it propose any protections for debtors against factors over which they have no control -- such as a sudden jump in interest rates or a sharp recession that would reduce demand for their products.

But the Baker plan does embrace a September agreement among the five major industrial nations -- the United States, Britain, France, West Germany and Japan -- that is aimed at reducing the high price of the dollar, stimulating economic growth in Europe and Japan and stanching the spread of protectionist sentiment in the industrialized world.

The Latin debtors long have argued that it is the economic policies in the West that are the root cause of their problems. It was U.S. anti-inflation policies that increased interest rates to astronomical levels and triggered the recessions in the early 1980s that sharply reduced Latin American exports and prices.

They also claim that it is the unwillingness today of Western Europe and Japan to take steps to stimulate their economies that holds down demand for the commodities that Latin America must export. Debtor nations also rail against protectionist trade policies in the industrial countries that they say undermine Latin America's ability to sell goods, even when the products are low-cost and high-quality.

At a debtors' summit in Montevideo, Uruguay, last month, the countries warned that they cannot endure their economic lot much longer. The industrialized countries must change their economic policies. Interest rates must be lower. World trade must increase.

In the interim, the 11 countries that make up the so-called Cartagena Consensus proposed their own "emergency plan" that goes well beyond the Baker proposal. They want commercial banks to boost their lending to the region by $12 billion to $13 billion a year. The debtors also want more long-term relief on their official debts to industrial countries and want a sharp increase in World Bank and Inter-American Development Bank lending, too.

The emergency plan will enable them to pay their debts on time, afford vital imports they cannot buy now and inject much-needed investment into their economies to build new factories and modernize existing ones. The plan is a bridge, to give the debtors relief until the industrial countries adjust their economic policies, the communique said.

The Montevideo communique also threatened "alternative measures" if the plan does not take shape. The communique did not spell out those measures, but Latin American officials privately said the only course they could follow would be the one most have rejected so far -- stopping some or all of their debt payments.

The threat was veiled and hardly pugnacious. But it revealed the frustration many countries feel after three years of trying to adjust to a world that has moved sharply against them.

"The conservatives are still in charge," said a top finance ministry official in one Latin American country. "But they are feeling the pressure of more radical elements on the left and the right."

"We'll continue to pay for a while, maybe even several years. But the creditor countries and banks have got to help," said another Latin American economic official.

But just as the Baker plan is silent on debt relief, the Montevideo plan does not address the types of economic "reforms" Baker called for in his pronouncement. Many of the reforms run counter not only to long-standing Latin American beliefs that the state should be a major economic agent, but also to fears of foreign investment that date back to colonial times.

But even before the Baker initiative, some countries were exploring the types of measures the U.S. Treasury Secretary advocated.

Argentina's Alfonsin -- with resistance from his own Radical Party appointees -- is opening up the oil industry to foreign investment, trying to force state enterprises to earn a profit and looking for state industries to sell. Brazil has sold a portion of the state oil company to private investors. Mexico is exploring ways to open up its highly protected and inefficient private industry to the rigors of foreign competition.

But any of these reforms will be slow and halting. And if countries appear to be making changes to capture Baker plan money, there would almost certainly be strong nationalist opposition.

"It's one thing to take crisis austerity measures, however painful they are," said one Latin American official. "It's another thing altogether to change decades of political and economic thought overnight. Many state enterprises have so many employes and managers that by themselves they present a political obstacle to change."