Reagan administration officials today bluntly rejected efforts by the European Community's chief trade negotiator to condition a new round of multilateral trade talks on the beginning of "parallel" talks on international monetary reform.

As bargaining over the details and the timing of a possible new trade round got under way today at the ministerial meeting of the Organization for Economic Cooperation and Development, a high U.S. official told reporters:

"There are plenty of things in the trade field that deserve attention regardless of international monetary issues. Therefore, the U.S. does not agree to linking trade and monetary issues. We need to address the trade issues now."

Treasury Secretary James A. Baker III, who spoke briefly on other issues today, will make a major speech Friday outlining the U.S. position.

While American officials hope that the effort to tie trade and monetary talks eventually will be beaten back, they admit that their strong drive to fix a date for beginning trade discussions has gotten bogged down.

In an impassioned plea to today's opening session, U.S. Trade Ambassador Bill Brock warned that without new multilateral trade negotiations, the international trading system will be "breaking down around us."

The best way for the 24 rich OECD industrial nations to show leadership, Brock said, "is to establish target dates for negotiations which these nations here present can support."

The United States, strongly supported by Japan and some other major countries, wants a preliminary meeting this summer, with actual negotiations to begin early in 1986.

Japanese Foreign Minister Shintaro Abe added that "if we leave it for any later, it will be very difficult to have any such round in the 1980s."

But at the end of a long day, American officials acknowledged that no date had been set, and it remains a question whether Friday night's final communique will include a date.

Some Europeans insist that a starting time is less essential than complete agreement in advance on the substance of the talks among all participants, including less developed nations.

The American view is that, to some extent, this attitude represents stalling by those Europeans who resist trade liberalization, especially in the areas of services and high technology, in which some European countries may believe that the United States and Japan have an edge.

The linkage issue was posed in the boldest terms by the European Community's chief trade negotiator, former Belgian finance minister Willy de Clerq.

At a press conference, De Clerc, whose formal title is external affairs commissioner for the European Community, said that the European Council of Ministers' March 19 declaration of support for a new trade round was conditioned on three developments: a rollback in existing trade restrictions; a significant reduction in Japan's trade surplus, and "parallel progress, parallel action" on launching monetary talks designed to stabilize currency relationships, especially the relationship of the dollar to other major currencies.

The actual March 19 text said that the other issues deserved "serious parallel consideration." The commitment to a new trade round seemed independent of these conditions, "subject to the establishment of an adequate prior international consensus on objectives, participation and timing. . . . "

In less than an hour, De Clerq was rebuffed by a key official of the International Monetary Fund, one of the agencies De Clerq had suggested as the overseer of "parallel" monetary talks.

H. Onno Ruding, chairman of the IMF's policy-making Interim Committee -- which will have its regular spring meeting next week in Washington -- said that he does "not believe in a strong link" between the trade and monetary goals.

Ruding, minister of finance for the Netherlands, is here for the OECD sessions. He argued that a close link "might paralyze both sides."

According to American sources, some Europeans -- notably the French -- are less interested in trade liberalization than in pursuing a long-time desire for a monetary conference that would put more stability into exchange rates.

De Clerq said the community's object was not to return to a fixed rate system in the pattern of Bretton Woods, "but to come to a system where erratic movements are under better control. Where you have a fluctuation of anywhere from 15 to 25 percent in the rate of the most important currency the dollar , you can speak of erratic movements."

De Clerq would not say that trade negotiations could not begin until monetary talks are under way.

"But we want parallel progress, parallel action -- the word parallel is important. . . . Trade negotiations will take a length of time, so there is reason enough to start negotiations on financial issues," he said.

As for American pressure to set an early date, De Clerq countered: "Let's start negotiating on all of the issues before" setting a deadline on trade talks.

When pressed on what was being demanded of Japan, the European commissioner said only that Europe's trade deficit with Japan had swollen in just a few years from $500 million to $11 billion a year, "and the time has come to call for results."

Commerce Secretary Malcolm Baldrige revealed that the communique will specifically call on Japan "to ensure greater market access." But American policy is not to precondition a trade round on further access to the Japanese market.

Abe, meanwhile, acknowledging the criticism of his country, somewhat bitterly laid some of the blame on the inadequacy of the efforts by foreign sellers in Japan.

"I should like to stress that market-opening can do no more than provide opportunities for free and fair competition," Abe said. "Is it not unfair to argue that the mere existence of a trade surplus proves insufficient market accessibility?"