Commercial banks, widely criticized for having lent too much money to Latin American nations in the late 1970s and early 1980s, will have to become major lenders again if the region is to return to anything approaching the prosperity it enjoyed in the late 1970s.

That is the conclusion that has been reached by top officials in the United States, in many other industrial countries, in the debtor nations themselves and even among many bankers.

An increase in commercial bank lending to Latin America appears to be a key part in a many-sided plan to revitalize the debtor countries that U.S. Treasury Secretary James A. Baker III is expected to unveil this week at the joint annual meetings of the International Monetary Fund and the World Bank in Seoul, South Korea.

Baker summoned top executives of the nation's largest banks to his Treasury office last Tuesday to brief them on at least part of the Treasury strategy. That strategy was born of the realization on the part of officials in both the Treasury and State Departments that, after three years of austerity in many debtor nations, growth and economic reform need more emphasis in the coming years.

But if the countries are to grow and continue to pay the interest on foreign debts -- which total about $360 billion -- they will need more foreign funds than they now are receiving.

U.S. officials also said they believe that there must be financial incentives to persuade debtor nations to make politically difficult economic reforms -- such as dismantling big state-owned sectors of the economy, opening up their economies to foreign investment and exposing inefficient domestic industries to the rigors of foreign competition.

The Baker strategy apparently involves stepped up lending on the part of multinational development institutions such as the World Bank and the Inter American Development Bank. The Treasury also wants these institutions to change their lending strategies to include more loans to countries that are making structural changes in their economies and more guarantees of private loans to encourage stepped-up commercial bank lending to the area.

The U.S. reportedly will support increased funding for the international lending agencies if they make such changes.

But there are far from enough funds in the official institutions to take the kinds of steps the United States envisions. As a result, the United States wants to encourage private commercial banks -- in the United States, Western Europe and the Far East -- to step up lending to Latin America.

Bankers, wary of throwing good money after bad, have been reluctant to make large-scale new loans to the debtor nations. About $230 billion of the region's $360 billion in foreign debt is owed to private commercial banks.

Banks have steadily eased the repayment terms on many of the debts and generally have made sizeable loans to countries once the countries sign economic agreements with the International Monetary Fund. But, after that, banks have been nearly as tightfisted as they were profligate in the late 1970s.

Now even some leading bankers have concluded that banks will have to join with governments and official institutions like the World Bank to increase the foreign resources available to Latin America.

"There will be a lot of resistance to new lending on the part of many U.S. regional banks and European banks," according to a top official of a major New York institution. "At the big banks Latin American loan officers will be opposed, too. Most of them think Latin American countries already have too much debt.

"But chief executives already realize they'll have to take the statesman approach and increase lending," the official said.

Willard C. Butcher, chairman of Chase Manhattan Bank, told reporters as much after meeting with Baker. He said Baker talked of the need to assure more growth in the world economy and conceded that "we are all in the same boat."

How much Baker wants commercial banks to lend in coming years is unclear. One New York banker said Treasury officials have talked of $20 billion in new bank loans -- beyond what the banks have already committed to lend -- during the next three to four years. The banker said that amount seems low.

Government officials decline to be specific about numbers. They said that commercial banks will be only one of several sources of funds -- including the multinational institutions, private foreign investment and credits from suppliers.

"Suffice it to say we are not going to be throwing money around, nor are we going to encourage international or commercial institutions to do so," said a top U.S. official.

John Williamson and Donald Lessard, in a recent study for the Institute for International Economics, estimated that Latin American nations need at least an additional $15 billion to $20 billion a year in foreign resources for the next several years. That would be far less than they were borrowing in the late 1970s but enough, the authors said, to allow them relief from the chokehold that the debt places on their economies.

Although many of the debtor nations have returned to economic growth in 1984 and 1985 -- after wrenching recessions in 1982 and 1983 -- they still must severely restrict their recoveries to husband dollars to pay just the interest on foreign loans. Most domestic industries must import vital components and spare parts, and if they expand too fast, their import requirements will eat up too many dollars.

The need to pay interest will become even greater when those industries need to expand and modernize. Chile, for example, must use nearly 8 percent of its total economic output to pay foreign creditors -- even though lenders have given Chile the easiest repayment terms and the most new loans of any debtor nation. Brazil, the most diversified and biggest of the debtor nations, pays the equivalent of 4 percent of its output to foreign creditors.

Officials of industrial countries said they have learned from the experiences of the 1970s, when they implicitly, and sometimes explicitly, encouraged heavy lending to enable developing countries to pay their skyrocketing oil bills. It took industrial countries off the hook of providing increased assistance to oil importing developing countries.

"I can remember the days in 1975 when all we could talk about was recycling petrodollars," recalled a former top economic official in the Ford administration. " Then Federal Reserve Chairman Arthur Burns kept saying that what you're also doing is creating debts."

What started off as recycling petrodollars to countries that in 1974 had little bank debt mushroomed into massive lending that, for a long time, seemed profitable to the banks and sensible to the borrowing countries.

The loans were being made in dollars -- whose value was steadily declining. That made the debts seem smaller and the dollars needed to pay it relatively easy to earn in an era of heavy inflation and rising commodity prices.

The debts became unmanageable when the dollar began to increase in value and commodity prices began to slide after stern U.S. moves against inflation.

The change in circumstances led to the Latin American debt crisis of 1982 -- a crisis that continues until today and that ushered an era of austerity into the region. In order to find the funds to pay foreign debts, most countries had to take steps to boost exports and draw savings away from their internal economies.

Many countries -- notably Mexico and Brazil -- managed to make these "external" adjustments rather successfully. But the cost was severe recessions followed by inadequate economic growth.

The countries have undertaken some economic reforms. Brazil is eliminating the use of subsidized credits; Mexico has liberalized some of its trade policies.

But the countries need to do more "structural reforms" to remove internal barriers to growth, and they "need to grow," according to a U.S. government official.

That is the point of the new U.S. plan, according to a top government official. "We are seeking policies more directed toward the promotion of growth rather than correction of external problems."

The new era will have less drama than the massive rescue efforts of 1982, 1983 and 1984 -- when bankers and industrial countries sought to keep enough funds flowing to the countries to avoid the kinds of defaults that could cripple the international financial system.

But the banks, pilloried in many quarters for their excessive lending in the 1970s, will be one of the key pillars of the new era.