Treasury Secretary Donald T. Regan and the finance ministers of four other major countries yesterday reiterated that they would intervene in exchange markets in a "coordinated" way "as necessary."

But the statement of the "Group of Five" financial leaders -- who have been meeting here for the past two days with International Monetary Fund Managing Director Jacques de Larosiere -- appeared to have offered no basic change in policies or procedures that some of the Europeans, buffeted by the extraordinary strength of the dollar, had hoped for.

Regan said after the meeting that the five "key currency" countries had agreed that they would intervene "when it would be helpful." In the past, Regan has consistently defined American policy as being willing to intervene only when exchange markets are "disorderly," not to try to reverse underlying market trends.

In the intervention process, a central bank buys its own currency in foreign exchange markets when it is going down, or sells it -- as would be the case at the moment with the dollar -- in an effort to bring it down.

"In light of recent developments in foreign exchange markets, [the ministers] reaffirmed their commitment made at the Williamsburg summit, to undertake coordinated intervention in the markets as necessary," a communique issued through the U.S. Treasury said.

At the Williamsburg summit in 1983, President Reagan and fellow heads of government agreed that finance ministers of the United States, West Germany, Great Britain, France and Japan would meet regularly with the IMF managing director to discuss coordination of economic and exchange rate policies.

But these meetings so far actually have produced little policy coordination. Since early 1984, the dollar has continued to rise sharply against most major currencies despite a decline in interest rates, and the huge American deficit has meant that American policy is more stimulative than in the other major nations.

The rise of the dollar and the decline of other currencies has been especially -- and politically -- painful for Great Britain, where the pound has slipped to less than $1.12, leading to the expectation that it may be reduced to parity with the dollar.

British Chancellor of the Exchequer Nigel Lawson, who participated in this week's meetings, told Parliament before leaving London that a continued decline in the pound would frustrate Britain's anti-inflation drive by pushing up the cost of imports.

What Lawson and his European and Japanese colleagues have been urging for some time more than intervention (which is regarded as a temporary palliative) is action to slash the American budget deficit. The deficit, they insist, causes high interest rates here that, in turn, keep the dollar too high.

Yesterday's communique by the group did not mention the U.S. budget deficit, but Regan reportedly outlined the administration's hopes for a major slash in the fiscal 1986 red ink.

The communique said the ministers would work toward "greater exchange market stability," by seeking "a convergence of economic performance at noninflationary, steady growth."

The statement also stressed the importance of removing "structural rigidities in their economies to achieving the objectives of noninflationary, steady growth and exchange market stability, and expressed their intent to intensify efforts in this area." The reference to "structural rigidities" is a code phrase for limitations on wage and work rules, or investment barriers thought to interfere with growth, especially in Europe.

Critics of the consultation effort first evolved at the Versailles summit in 1982 say that to make the pledge of policy "convergence" meaningful, the major powers have to agree to a greater degree of multilateral surveillance by the IMF.