President Reagan, in a private meeting with West German Chancellor Helmut Kohl prior to the opening tonight of a seven-nation economic summit, told the German leader today that "we do not condemn the Germans as a nation" for Nazi atrocities in World War II.

In what was described as a gesture of historical reconciliation meant to mark the 40th anniversary of the end of World War II, U.S. officials briefing reporters said Reagan told Kohl that the United States and its allies abandoned the idea of "collective guilt" for war crimes in the 1946 Nuremberg trials.

The president also reportedly told the chancellor that he had never wavered from the plan to lay a wreath Sunday afternoon at a German military cemetery at Bitburg where 49 members of Adolf Hitler's Waffen-SS Corps are buried along with about 2,000 other German soldiers. In the three weeks since the visit was announced, it has provoked an uproar among Jewish and other religious leaders, veterans' groups and Congress that has strained U.S.-West German relations and has overshadowed all other aspects of Reagan's trip abroad.

Kohl's government announced today that the two leaders would be joined at the cemetery by four members of the anti-Nazi German resistance and their relatives, including West German Army Col. Berthold Stauffenberg, whose father tried to assassinate Hitler in 1944 by placing a bomb in his headquarters.

The chancellor responded to Reagan's statements today by praising his courage for sticking by his promise to appear at the cemetery with Kohl despite intense political pressures. Kohl told Reagan, according to an account by a U.S. official, that his decision to stick to the visit plan "has sent a very powerful message to the German people" and that Reagan's popularity was such that if he ran for election in West Germany he would win by a wide majority.

The American commander of a big U.S. air base at Bitburg also said that U.S. and West German military commanders had been laying wreaths annually at the same cemetery for years to honor all military dead.

In Paris, however, the French secretary of state for European affairs, Catherine Lalumiere, told the National Assembly today that the French government "shares the emotion" stirred in public opinion by Reagan's decision to visit Bitburg.

Reagan also was chided gently by British Prime Minister Margaret Thatcher, whom he called "my friend Margaret," over his Bitburg visit. She said in a Wall Street Journal interview published today that while all the western leaders share Reagan's belief in reconciliation, "our motives would have taken us in a different direction."

As part of an effort to defuse the crisis, West Germany offered Reagan an extraordinary diplomatic platform yesterday for his announcement just after landing here that he was imposing a total trade embargo on Nicaragua.

West German officials, while reserving judgment on the sanctions, said they were informed in advance "exactly what Washington intended to do." They said Kohl fully approved of Reagan making the announcement at the start of his visit in the apparent belief that it would help shift attention from the furor over the Bitburg appearance.

Expressing his gratitude for Reagan's steadfastness, Kohl strongly endorsed the president's controversial antimissile research plan, popularly known as "Star Wars," and backed Reagan's call for a new round of global trade liberalization talks "as soon as possible."

But Reagan still faced difficulties in winning unanimous approval of his call for early trade talks.

French President Francois Mitterrand, in a meeting with Reagan, reiterated his objections to fixing a firm date for the new trade talks on the ground that the precise agenda for the negotiations and the participants have yet to be determined.

Commenting on differences between Reagan and Mitterrand over strategic defense and trade, French presidential spokesman Michel Vauzelle said, "It's an old French peasant instinct not to agree to anything until you know exactly what you're being asked to approve."

It appeared today that only France, with some support from Italian Prime Minister Bettino Craxi, was intent on linking the global trade talks with progress on monetary reform. The expectation among U.S. officials was that the French were likely to stick to their position on trade talks.

A British spokesman said Thatcher shared Reagan's view that a rising tide of protectionism is the dominant issue of the summit and backed the president's plan for starting the new round of trade talks in early 1986.

As the leaders gathered for an opening dinner tonight at the Falkenlust Castle, political matters were high on the agenda, including East-West relations, the Geneva arms talks, Central America and Reagan's missile defense plan, formally known as the Strategic Defense Initiative (SDI).

At the summit working sessions, which open Friday morning, trade issues were expected to dominate the discussion, along with a search for ways to sustain world economic expansion while the U.S. economy appears to be slowing down.

After two hours with Kohl, Reagan met with Japanese Prime Minister Yasuhiro Nakasone, Mitterrand and Thatcher at the official U.S. diplomatic residence here. It was a day of photo sessions, which Reagan began by reviewing West German troops in a blustery cold wind at Villa Hammerschmidt, the official residence of West German President Richard von Weizsaecker.

Reagan's appeal for support for his strategic defense program loomed as the most controversial political topic at the three-day summit. West Germany, Britain and Japan have said they are receptive to joining the research program, but want assurances that they will be able to share fully in its findings.

Kohl explained that West Germany first wants to explore the possibility of a joint European approach to SDI before committing itself to the U.S. program. West German spokesman Peter Boenisch said, however, that the search for a European consensus must not be allowed to impede research progress.

"Other Europeans are heartily welcome as partners, but not as a brake," he said.

Thatcher came to the summit backing Reagan on SDI research.

France has expressed skepticism about U.S. willingness to share the results of SDI research with its allies. Secretary of State George P. Shultz said today, after the Reagan-Mitterrand meeting, that he did not see any indication that the French intended to participate.

Mitterrand's spokesman confirmed those doubts by raising a series of questions about the U.S. program that Paris would like answered before responding to the U.S. offer to participate. These included cost for the Europeans, distribution of potential benefits and the precise content of the research.

The French have proposed a pure research program called "Eureka," designed to boost European research efforts in similar areas to those covered by SDI.

Reagan has made SDI a high priority in his private discussions with other leaders, but it is uncertain whether he will seek a formal statement of support in the political declaration that Bonn wants to use to emphasize the themes of peace and reconciliation.

In their discussions on the Bitburg controversy, a West German official quoted Reagan as saying he "regretted" the outcry in the United States among Jewish and veterans' groups. But White House officials said they had not heard Reagan make any such comment.

Reagan and Kohl also continued to try to overcome the controversy over the Bitburg visit by stressing the importance of a younger, post-World War II generation to German-American relations.

Kohl said in a television appearance that Reagan wants the Bitburg visit perceived as a gesture of friendship for Germans, and particularly the nation's youth.

The approaching May 8 anniversary of the Nazi surrender has been causing anguish among West Germans trying to cope with the postwar division of their nation. Today, Reagan sought to soothe West German anxieties by stressing the accomplishments of a prosperous, democratic country firmly wedded to the Atlantic Alliance.

Reagan told Kohl that May 8 "marks not only the end of World War II and Nazi barbarity but also the beginning of a new partnership in Europe," a Bonn official said.