The United States and its major allies are charting a new course to save poor nations from collapse and to prod rich industrial powers out of recession. The agreement, reached in Paris by leading Western nations - the so-called Group of Ten - involves a two-track operation:
* The 10 powers will make more money available to ward off default by developing nations so deeply in debt that some cannot meet their obligations without special help.
* The rich nations - especially those that have made the most progress against inflation - will try to take steps to stimulate their own economic growth.
This departs from the policy prescription of the past several years, when most Western governments focused on fighting inflation.
Notable gains have been made against inflation in a number of countries, including the US, where the inflation rate has been cut in half over the past two years. Among the West's 24 leading industrial powers, the Organization for Economic Cooperation and Development reports, inflation over the 12 months ending last November dropped to 6.9 percent - the first yearly rate below 7 percent since early 1973.
A consequence of the anti-inflation battle, however, has been the worst global recession since World War II, including high unemployment throughout the industrial world. When rich nations have economies that are stagnant, they buy fewer goods and commodities from developing countries, which worsens the debt problems of the latter.
Altogether, says Treasury Secretary Donald T. Regan, foreign debts owed by third world countries have mushroomed to more than $500 billion - ''five times the level of 1973.'' Roughly 60 percent of this debt is owed to private Western banks, the rest to governments and international lending agencies.
''By June of 1982,'' Mr. Regan says, ''the stock of debt owed to private Western banks by non-OPEC developing countries had grown to about $265 billion, of which almost $170 billion was owed by countries of Latin America.'' Mexico and Brazil head the list, with debts of $80 billion each. Then comes Argentina, with more than $40 billion, followed, Regan says, by ''a long list of other nations with huge debts.''
Extraordinary efforts are being made by creditor banks - the International Monetary Fund (IMF) and central banks of Western governments - to reschedule debt repayments by some hard-hit nations, including Mexico, Brazil, Poland, and Yugoslavia.
But rescheduling is a palliative. Recovery for poor nations cannot come until recovery starts among the rich, thereby expanding markets for foreign trade.
Against this background, Secretary of State George P. Shultz - supported by Mr. Regan - urges that key industrial powers, including the US, adopt expansionary policies to break out of recession. This is in line with current efforts by the Federal Reserve Board to nudge US interest rates lower, thereby stimulating the American economy.
An expansionary theory, says international trade consultant Harald B. Malmgren, risks ''a little inflation,'' on the grounds that the risk of world depression is greater.
Nothing formal was decided on this score by the Group of Ten in Paris. Each government must determine what it can, or will, do to stimulate its domestic economy.
If a major aim of the expansionary theory is to open home markets to more goods from developing countries, it comes at an awkward time. Already, with unemployment at post-depression highs in Western Europe and the US, protectionist pressures are intense.
Employers and workers in troubled Western industries - notably autos, steel, and textiles - are pressing their parliaments to curb foreign imports, not expand them.
The US and China, for example, find themselves suddenly in a mini-trade war over Washington's limitations on imports of Chinese clothing and textiles.
Some experts predict a possible contradiction in the policy now being worked out within the Group of Ten. The IMF, a lender of last resort to debt-burdened nations, requires as a condition of loans that debtor borrowers adopt policies of economic austerity. This includes, among other things, curbs on nonessential imports and diversion of the money thus saved to paying off debts.
This policy, while backed by the US and other major lenders, means that poor lands will buy fewer goods from industrial powers. Already this is happening to the US, which finds American exports to Mexico and other Latin American debtors sharply reduced.
Because third world nations, including OPEC members, buy 38 percent of all US exports, a slump in this market makes it harder for the United States to shake off recession.
Still, economic growth among industrial nations would boost their demands for raw materials and commodities normally supplied by third world countries. This would help a number of debtor nations earn additional foreign exchange.
Measures adopted by the Group of Ten to help debtor lands break down as follows:
* The 10 richest nations agreed to expand from $7.1 billion to $19 billion an emergency pool of money, called the General Arrangements to Borrow. This ''crisis fund,'' maintained by the Group of Ten, would be available to any IMF member experiencing problems that threatened the stability of the international monetary system.
* The Group of Ten agreed also to boost substantially the resources of the IMF - quotas of loan capital made available by each of the fund's 146 member states. The exact amount of the new quotas will be decided at an IMF policy board meeting in Washington next month.