Martin S. Feldstein, chairman of the Council of Economic Advisers, yesterday challenged the "conventional wisdom" that the U.S. dollar is overvalued, and argued that the government should not take steps aimed "at lowering the dollar's value."

Treasury Secretary Donald T. Regan had said two weeks ago that the administration "would like to see a somewhat weaker dollar in order to help our exports. But that doesn't mean we're going to do anything about it."

In a speech to the Council on Foreign Relations in New York, Feldstein took issue with the common complaint by American business officials that an overvalued dollar is a major reason for their difficulty in competing with imports--notably from Japan. It is "difficult to define, and even more difficult to defend," the concept of an overvalued dollar, he said.

In addition to complaints from business officials in the United States, there have been suggestions from European nations whose currencies have weakened against the dollar that joint efforts be made to stabilize exchange-rate relationships. It is clear that the idea will be proposed formally at the Williamsburg, Va., economic summit to be held at the end of May.

It is equally clear that Feldstein, as one of Reagan's important economic advisers, will counsel against such a step.

Contrary views to Feldstein's were expressed yesterday at a hearing before the Senate Foreign Relations Committee, where former Treasury assistant secretary C. Fred Bergsten said that "the continuing substantial" overvaluation of the dollar in respect to the Japanese yen is the most critical economic problem facing the United States.

Lee L. Morgan of Caterillar Tractor Co., representing the Business Roundtable, also told the committee the United States and the International Monetary Fund should investigate Japanese policies that he said allows them "an unfair competitive advantage."

Bergsten recommended Japanese limitations on institutional capital outflows, and joint exchange market intervention by the United States and Japan.

In his speech, Feldstein conceded that the current exchange rate is failing to balance imports and exports: The merchandise trade deficit this year may exceed $60 billion, he predicted. Also, the current account deficit, which includes payments for services, and interest and dividends from overseas, could hit $25 billion this year.

"By that standard, the dollar is currently overvalued," Feldstein said. "But why should we expect or want a current account balance in every year?" he asked.

According to his analysis, the current high exchange rate of the dollar is produced by the anticipation of huge federal budget deficits, which in turn cause real interest rates to go up. The real interest rate increases boost the value of the dollar, and thus cause the larger trade deficit (as U.S. goods are marked up).

"In short, budget deficits beget trade deficits, and this requires a high exchange value of the dollar," Feldstein said.

A weaker dollar would boost exports and reduce imports, but also would reduce the capital inflow from the rest of the world, Feldstein said. His conclusion was that "the rise in the dollar is a safety valve that reduces pressure on domestic interest rates; the increase in the trade deficit allows the extra demand generated by the budget deficit to spill overseas, instead of crowding out domestic investment."

The only "appropriate" way to cut the adverse trade balance is to get the federal deficit itself down, Feldstein said.