The U.S. trade deficit could be substantially reduced if the Third World debt crisis is defused sufficiently to allow middle-income developing countries to become important customers for American products again.

That is a central conclusion of a new policy study by the Overseas Development Council, a local think tank devoted to debt and development issues in less advanced nations.

The report argues that the next U.S. president will be faced not only with the tough assignment of restoring the United States' domestic strength, but with fundamental changes that now bind America's future inextricably "with the progress of the developing countries."

It also contends that for the longer run, policymakers in both the rich and poor nations must deal with the potential impact of an impending "third industrial revolution," based on new and complex technologies that will be more difficult for the poorer nations to introduce and manage. That could further harm many Third World countries, "an outcome that would not be in either the economic or political interests of the United States," the report says.

The ODC study, edited by ODC President John W. Sewell and project director Stuart K. Tucker, acknowledges that under any set of assumptions and circumstances, "the {U.S.} trade deficit will not disappear quickly." But it suggests that if the growth rate in the Third World can be expanded from currently projected levels of less than 3 percent to 6 percent, an additional $32 billion might be lopped off the U.S. trade deficit by 1992.

But such a growth rate -- more in line with the period of great Third World expansion in the 1960s and 1970s -- can not be expected, the authors say, unless "the import restraints on the debtor countries imposed by the debt crisis were released."

It cites Commerce Department data showing that the U.S. trade deficit with all developing countries increased from a $3.3 billion in 1975 to $31 billion in 1981 and $57.2 billion in 1986. An actual surplus of $1.3 billion with Latin America in 1981 degenerated into a $13 billion deficit in 1986.

The report cites "conventional wisdom" that the huge existing trade imbalance can be corrected by depreciation of the dollar, assuming at the same time that Japan, West Germany and other industrialized countries expand their domestic economies.

That is the strategy pursued by the so-called Group of Seven nations. But leaders in those countries -- the United States, West Germany, Japan, France, Britain, Italy and Canada -- almost never consider the vital role played by the middle-income debtor countries, the report says.

"Policies to expand U.S. growth, exports and jobs must also include measures to restart the progress in our major Third World export markets," Sewell said. According to the report, the economic downturn in the Third World cost the United States more than $60 billion in exports and 1.7 million jobs from 1980 to 1986.

Sewell and Tucker predict an actual increase in the U.S. trade deficit to $198 billion in 1992, assuming a U.S. economic growth rate of 3.1 percent from 1989 through 1992, growth of 2.8 percent in the Third World and 2.9 percent in key industrial countries outside the United States, and no change in the value of the dollar or other basic conditions from the end of 1986.

Using the same 3.1 percent U.S. growth estimate, an improvement in global growth elsewhere (including a 4.7 percent rate in the Third World), a continued fall in the value of the dollar -- but no change in management of Third World debt -- the report projects a $112 billion trade deficit by 1992. That would boost the U.S. external debt burden from $400 billion at the end of 1987 to $650 billion in 1992.

But if the relatively high global growth of the above scenario were accompanied by enough debt reduction in the Third World to push the growth rate to 6.1 percent, the report says, the U.S. deficit could be sliced by an additional $32 billion to $80 billion in 1992.

And if, on top of that, American companies were able to boost their competitive edge in Third World countries, increasing their share of imports relative to other suppliers, the trade deficit could be trimmed by another $11 billion to $69 billion in 1992.

Another way to reduce the U.S. deficit would be to suffer a mild recession of the magnitude of the one in 1981-1982, the authors say. That could cut $40 billion to $50 billion from the projected $198 billion total by 1992. But the costs of a U.S. recession would be enormous, the authors say, including disastrous effects on the economic and political stability of the developing world.