The National Association of Manufacturers, in a pessimistic assessment of the international competitiveness of U.S. industry, said yesterday that this nation's position in the world economy is eroding rapidly and blamed the strength of the dollar against foreign currencies for much of the decline.

Lawrence Fox, NAM's vice president for international economic affairs, released a study showing that the United States is losing ground in trade in almost every kind of manufactured goods. Overvaluation of the dollar is the "most important single factor," Fox said, calling for an end to the floating-exchange-rate system adopted in 1973.

With the dollar overvalued against the yen and mark by as much as 25 percent, the administration should seek to abandon the float in favor of a negotiated "target-zone system" that would set a fixed range of value for the yen and the mark, Fox said.

He said the dollar is "now more overvalued than at any time since 1971," and the current exchange rates are "totally out of line with the better performance Japan and Germany have demonstrated in improving their productivity, holding down inflation and increasing their exports of manufactured goods."

As a result, he said, Japanese and German manufacturers have a built-in price advantage in world markets, making it "extremely difficult" to reverse what the NAM called "the steady decline in our overall trade competitiveness."

The NAM released data showing that although U.S. payments for foreign oil declined between 1981 and 1982, that was offset by declines in exports of American farm products and manufactured goods.

Fox argued that exchange rates in the free market do not reflect the relative strengths and weaknesses of the U.S., Japanese and West German economies, but are a result of high interest rates here that attracted foreign capital and "rewarded it for coming."

"The floating exchange rate lends itself to being overwhelmed by capital movements," and should be replaced by an agreement to hold the yen at 200 to the dollar and the mark at 2.15 to the dollar, give or take 5 percent, he said. The current rates are 236 yen and 2.43 marks.

At the same time, the U.S. Chamber of Commerce, another major business group, released a package of trade proposals that included "harmonization" of economic policies between this country and its trading partners, aimed at "reducing exchange rate distortions."

Michael Samuels, the chamber's international vice president, said in a luncheon meeting with reporters that "there is an exchange-rate problem" underlying the nation's record $36.1 billion merchandise trade deficit in 1982. But Samuels said that the way to deal with it is "not to deal with exchange rates alone," but to "coordinate with key countries on their domestic economic policies," as the chamber recommended in its paper.

The chamber also called for negotiations to improve U.S. access to foreign markets, liberalization of restrictions on exports, government action to enforce and improve existing world trade agreements and increased funding for the Export-Import Bank. The NAM also urged expansion of the Ex-Im Bank.

Both groups took strong positions against protectionist legislation. Fox, speaking for the NAM, said "protectionist legislation has to be avoided" because "two-thirds of the problem" of the decline in merchandise trade "is in the relatively poor performance of our domestic economy," not the result of improper action by foreign competitors.

The chamber said the United States "should not take measures which have the effect of restricting or discriminating against . . . imports in a manner inconsistent with U.S. commitments under international agreements."

Fox's call for limitations on foreign exchange rates is unlikely to find much support in the administration. The issue was discussed at length in the annual "Economic Report of the President," which said that large trade deficits are caused mostly by large budget deficits.

Attempts to juggle the exchange rate may help some sectors of the economy but hurt others, the report said. "That governments cannot simultaneously protect everyone is a basic principle of international trade," it said.