PRESTON MARTIN has taken the right and honorable step in resigning from the Federal Reserve Board. He had created an intolerable situation there, and he has now taken the initiative to end it.

As vice chairman of the board, Mr. Martin was campaigning openly to succeed Paul Volcker as chairman. In the famous Feb. 24 meeting, he led three other Reagan appointees in defeating Mr. Volcker, 4 to 3, on the crucial issue of interest rates. Mr. Martin's majority, fortunately, did not last through the day. Another member, Wayne Angell, had second thoughts and reversed his vote before the change was announced. But when this incident was reported last Monday by Rowland Evans and Robert Novak in their column, it revealed a disquieting degree of division and instability in the board.

The Federal Reserve board generally operates through a broad consensus with the chairman as its spokesman. It is extremely rare for the chairman to be outvoted in the board, and always a sign of serious trouble. The Federal Reserve is in constant conversation and negotiation with other countries' central banks, and other governments cannot be allowed to doubt that the chairman speaks for the United States. The management of the international monetary system is particularly demanding currently, for the exchange rate of the dollar is falling with unusual speed. The prosperity of this country, and many others, depends on the skill and sureness with which the dollar is brought to a landing.

It is hard to know precisely what Mr. Martin intended by organizing the vote against Mr. Volcker. Presumably he meant to challenge and constrain him, perhaps even to force him out of office. In fact, he succeeded in weakening the United States by creating doubt and uncertainty about American intentions where there was none before.

By departing, Mr. Martin spares the country an endless and corrosive stream of gossip and speculation about the shifting lineup among the board's seven votes. He diminishes the prospect of constant counts and recounts of threes and fours among investors and bankers, here and abroad, as they anxiously try to calculate whether American monetary policy will stay firm or collapse. Mr. Martin cannot restore the previous assurance. That is not within his capacity, or anyone's. But he has done, promptly and gracefully, the one thing that he could usefully do. He has resigned.