By JONATHAN FUERBRINGER

Published: September 23, 1988

After winning another battle this summer, the world’s industrial democracies are beginning to offer convincing evidence that, more than before, they can influence the course of the volatile foreign-exchange markets.

In the three years since their historic Plaza Hotel agreement, the finance ministers of the United States and its allies have deftly intervened in the markets with coordinated purchases and sales of dollars and other currencies with repeated success and few failures. And, more important, they have backed up their actions with economic cooperation that has finally given their intervention, often ineffective in the past, some real thrust. Avoiding Disruptive Swings

With such coordination, there is a better chance that the world financial system can avoid the disruptive swings in the dollar, whose ups and downs affect the price of everything from vacations to exports, that have occurred since currencies were allowed to float freely in 1973. These swings can disrupt economies, make a country’s exports less competitive abroad and stir general talk of trade retaliation.

»When you look back 10 years from now, this will be one of the best-managed exchange rates in a long time,» James T. McGroarty, vice president of the Discount Bank of New York, said of the last three years. »It’s been intriguing to me. I was slow in recognizing how the Plaza changed things.»

The latest test of the Plaza accord came this summer when a dollar rally appeared to be getting out of hand, forcing the cooperating governments to step in with billions of dollars of market intervention. By September, however, the dollar, was in harness again. The intervention had gained enough time for a changing economic outlook and coordinated interest rate actions to mute traders’ bullish talk.

Indeed, as the finance ministers of the world gather for meetings of the International Monetary Fund and the World Bank in West Berlin this weekend, intervention is again seen as one of the important management tools used to influence the course of the 24-hour currency markets, which daily churn out more than $400 billion worth of trades around the world. But the debate about the effectiveness of intervention continues because some traders and economists still doubt that even billions of dollars of intervention can move a market that is a hundred times larger.

After being shunned as ineffective during the first four years of the Reagan Administration, intervention returned to center stage as part of the accord on foreign-exchange policy reached at the Plaza Hotel in New York three years ago yesterday. 4 Episodes of Intervention In the four major episodes of intervention since then, during which the United States sold or bought more than $16.7 billion and other central banks spent billions more, one helped turn the dollar around, one helped it decline sharply and the third tried, but failed, to support the dollar. The fourth big effort was this summer.

The immediate aim of the Plaza meeting was to get the United States, France, West Germany, Britain and Japan to cooperate in a major effort to push down the value of the dollar.

More important, the Plaza agreement marked a new attempt at economic cooperation in which the United States and its allies would shape their fiscal and monetary policies with regard for their international consequences. Better coordination can prevent disparities — like trade imbalances — that can send a currency up or down sharply.

This new cooperation makes a difference. Unlike periods of intervention in the 1970’s, when it could be uncoordinated and isolated, intervention is now orchestrated and better guided by cooperative economic goals. Changes in economic policies, such as a rise in interest rates, often back up the initial push of central banks’ intervention.

This makes intervention, said Craig S. Shular, manager for foreign-exchange risk at the Union Carbide Corporation, a warning of policy shifts that the market has to heed.

Just this summer, intervention in the markets was backed up by an interest rate increase in West Germany at the end of August. That move weakened the dollar against the mark as more foreign investors bought bonds denominated in marks. Wary of the Central Banks

»Intervention now would be perceived as a unified front, and if it is not successful at the beginning it will be leveraged up and become successful,» Mr. Shular said. »That is what has got us stuck in this tight range now. Eighty percent of the market wants to be long dollars now, but that 80 percent doesn’t want to take on the central banks.»

Richard E. Witten, vice president for foreign exchange at Goldman, Sachs & Company, said nations’ cooperation has given intervention »an enormous amount of more clout.»

The United States intervenes in the foreign-exchange markets when it buys or sells dollars — buying to support the dollar and selling to weaken it. The decision to intervene involves the Treasury, the Federal Reserve Board and the Federal Reserve Bank of New York, which carries out the intervention operation.

The reasons for intervening vary. As was the case this summer, it can be an effort to stop a rise of the dollar. The central banks try to send traders a message about dollar policy.