Washington — Much of the world's tangled economic situation revolves around a problem that clouds the prospects of rich and poor nations alike. Developing countries, many of them sinking under massive debts, must export their goods - both commodities and manufactures - if they are to have any hope of repaying the enormous sums they owe to Western banks.
The most important markets for those exports are the economies of the so-called ''northern tier'' of rich industrial powers - the United States and Canada, Western Europe, and Japan.
''We have to open up our markets further (to developing countries) or they will not be able to repay their debts,'' says Robert Lighthizer, the deputy US trade representative,.
Otherwise, Mr. Lighthizer says, ''we will be creating the kind of crisis which we are trying to avoid.''
He meant the risk of default by one or more debtor nations, which - if it happened - could shake the stability of the world's banking system.
''The (developing countries),'' says international economist C. Fred Bergsten , ''need export growth at least equal to the rate of interest on their debt, or else they will be constantly falling behind in their capacity to repay.''
No one argues with this in principle. The problem is that many exports from less developed countries (LDCs) - produced more cheaply than industrial powers can make them - throw people out of work in the US and Europe.
Industrial jobs lost because of imports from the third world, former World Bank president Robert S. McNamara says, number in the millions.
Western nations, experts agree, face increasing competition from a broader and more sophisticated range of exports from LDCs in the years ahead.
This is inevitable as advanced developing nations - Taiwan, South Korea, Singapore, Brazil, Mexico, and others - climb the industrial ladder that Western nations mounted long ago.
With 32 million people out of work in the 24 nations of the Organization for Economic Cooperation and Development - and with the jobless toll still rising - the demand is for more, not less, protection from foreign goods.
Most Western leaders, President Reagan among them, oppose protectionism. In practice, however, they succumb to political pressure from powerful interest groups and allow free trade to be nibbled away.
The US, for example, limits imports, in one way or another, of Japanese cars, European steel, textiles from China and other developing lands, beef from Australia, and so on.
The curbing of imports hits hard at consumers, who are denied a wider choice of goods and must pay more for what they can buy. US manufacturers, to the extent they are shielded from cheaper foreign competition, are relieved of the need to lower their own prices.
''My real objection to import curbs,'' former presidential adviser Murray Weidenbaum says, ''is what I call consumer welfare. Protectionism costs money and is inflationary.''
The Japanese, to take one example, deliver a small car in the United States about $1,000 cheaper than Detroit can build one, partly because Japanese steel costs $100 a ton less and partly because Japanese labor costs are lower.
The quality of Japanese cars is widely appreciated by US buyers. If Japan were free to sell all the cars it could in the United States, Tokyo's share of the US market very likely would rise.
Factors of price and quality influence consumer decisions in many areas. Families of US auto workers, while sticking to American cars, may well buy TV sets, cameras, radios, and wearing apparel made overseas.
Americans export more goods to developing countries than they do to Japan and Western Europe combined. LDCs provide the fastest growing markets for US exporters.
Jobs for Americans, in other words, depend on growing economies in the third world. Mexico's cutback on imports of US products last year is estimated to have cost more than 100,000 US jobs.
''US exports to key developing countries during the period 1970 to 1981 grew 20 percent a year,'' says Lighthizer. ''With the debt problems of these countries, US exports to them fell by 28 percent in 1982.''
In the United States, meanwhile - partly because of growing competition from LDCs - the number of jobs in auto, steel, textile, footwear, and some other industries declined sharply.
No one has easy answers to these intertwined problems, except for general agreement that alarm bells are ringing on debt burdens of the LDCs.
''The single most essential thing we can do at the moment.'' says Allan E. Gotlieb, Canada's ambassador to the US, ''is to improve economic conditions in industrial countries,'' thereby widening export opportunities for nations of the third world.