PARIS, JUNE 18 -- Growing trade tensions and debt problems have made it more likely the world's economy will slow further, the Organization for Economic Cooperation and Development said today.

The group also reduced its estimates of economic growth this year in the United States, West Germany and Japan, the world's three most powerful industrial countries.

The group, whose members consist of the 24 noncommunist industrialized nations, said those nations needed to produce concrete actions to back up promises from Western leaders of greater coordination on economic concerns.

In its semiannual study of the world economy, the OECD said concerns about fluctuating exchange rates already have eroded confidence to the point that exporters are hesitant to invest in trade.

Fears of a tighter U.S. monetary policy to prop up the falling dollar also seem to be depressing sectors of the U.S. economy that are sensitive to interest rates or tied closely to Third World debt problems, the report said.

These factors, along with trade tensions, "have increased the risks of a worsening world economic situation," the OECD said.

The OECD's warning was accompanied by a downward revision of growth prospects for the three leading economies.

The forecast for growth in the U.S. economy was scaled back to 2.5 percent for 1987 from the 3 percent pace projected at the end of last year. The forecast for Japan was cut to 2 percent from 2.8 percent, and the outlook for West Germany was cut in half to 1.5 percent.

The OECD's forecast for 1988 was not much brighter. It predicted growth of 2.75 percent in the United States and 2 percent in both Japan and West Germany.

The report urged political leaders to fight protectionism, cut farm and industrial subsidies and increase the role of market forces.