Former president Richard M. Nixon privately urged President Reagan last week not to back down from plans to visit the German military cemetery at Bitburg where 49 Nazi SS soldiers are buried, according to informed administration sources.

Nixon, whose views were solicited by senior White House officials, is reported to have said the planned cemetery visit had caused "substantial domestic political damage" but urged Reagan not to bow to protests from groups representing Jews, veterans and others to cancel the appearance.

White House sources also said that former secretary of state Henry A. Kissinger had urged Reagan to go ahead with the planned visit May 5, citing the importance of relations with West Germany.

Nixon's advice came as 257 House members wrote West German Chancellor Helmut Kohl last week urging him to withdraw the invitation and 82 senators urged Reagan in a resolution to reassess the Bitburg visit.

The White House has been searching for ways to dampen the controversy. Chief of staff Donald T. Regan said yesterday the Bitburg cemetery visit is now scheduled to last only 10 to 15 minutes, while the president will spend "over an hour or even longer" at the Bergen-Belsen concentration camp earlier the same day.

The concentration camp visit was added to Reagan's itinerary -- after he said publicly he did not want to make such a stop -- in response to protests over his plans to lay a wreath at the Bitburg cemetery, where 49 of Hitler's elite storm troopers are buried with about 2,000 other German soldiers from both world wars.

In a meeting with aides earlier this year, when the West German trip was in its planning stages, Reagan ruled out a visit to the Dachau death camp, according to a White House official.

Reagan is to leave Tuesday for a 10-day European tour that begins with the seven-nation economic summit in Bonn. It will be followed by a two-day state visit to West Germany. Both are intended to strike a theme of reconciliation 40 years after the war in Europe ended.

Reagan's tour will also include state visits to Spain and Portugal and a speech before the European Parliament in Strasbourg, France.

Yesterday, Regan said the president is "anguished" and "wounded" by the controversy over the visit to Bitburg.

"The president's been quite upset, as he's been a staunch friend of Israel," has sought freedom for Soviet Jews and has ordered U.S. assistance in the airlift of Jews from Ethiopia, Regan said on CBS-TV's "Face the Nation."

"The president feels that being a friend as he is to Jews everywhere -- to have this now overshadow a state visit is distressing," Regan said.

Regan said the president could not change plans to visit Bitburg. "He's carrying out his word" to Kohl, Regan said.

Nixon occasionally is in contact with Secretary of State George P. Shultz and national security affairs adviser Robert C. McFarlane, and has been asked to advise Reagan on other occasions.

Nixon said it would be a sign of weakness for Reagan to change his itinerary now, according to one official, who spoke on the condition he not be identified.

Nixon said a reversal of the Bitburg plans would undermine Reagan's standing with the Western European allies and his ability to negotiate with the Soviets and in the Middle East, this official said.

"The credibility of future negotiations is at stake," Nixon is reported to have said.

Nixon encouraged Reagan to use his appearances at Bitburg and the Bergen-Belsen concentration camp to "frame the visit in his terms" and deliver a dramatic and emotional address, the official said.

Nixon, while acknowledging that the trip controversy had caused significant political damage in the United States, said he thought "the damage is done" and could not be remedied by a switch in plans now.

Sen. Arlen Specter (R-Pa.) said yesterday "I'm still hopeful" Reagan will change his plans and said the White House has underestimated the U.S. reaction to the Bitburg visit.

Specter charged that the Kohl government failed to inform the White House that Nazi SS soldiers were buried at Bitburg. If Kohl does not withdraw the invitation, Reagan should cancel the cemetery visit, saying he made the plans "on wrong information," Specter said on the CBS program.

Alois Mertes, West German deputy foreign minister and a member of parliament from the Bitburg area, said he rejected the senator's charge that the Kohl government had misled the White House.

Mertes said the Senate resolution approved last week upset many Germans and was an "insult against all German people who were soldiers. This implies we were all Nazis . . . . What we are doing is mourning all the dead."

Mertes said protests in the United States are imposing a "partial collective condemnation which is not justified" on today's West German population.