The West German ambassador appealed yesterday to Jewish groups to join hands with "the new Germany" in a mutual struggle "for human dignity and a better world."

Speaking to the board of governor's of B'nai B'rith International, Ambassador Guenther van Well denounced the Nazi dictatorship that caused the slaughter of approximately 6 million Jews throughout Europe. That regime "taught us a lesson like no other lesson a nation can be taught," he said.

Now, with "a new totalitarian ideology" -- of the Soviet Union -- "challenging our common Western culture and civilization rooted in Judeo-Christian values," van Well said, "let the terrible past and the dangers of the present guide us towards recognizing our common goals and interests."

Asked by the Jewish organization to discuss the "German-Jewish Relationship After Bitburg," the ambassador made only glancing references in his address to President Reagan's controversial visit to a West German cemetery where German soldiers, including some Nazi storm troopers, are buried.

Noting the common commitment to human rights shared by his government and Jewish groups, van Well said: "Let us help each other and strengthen each other. Let us build a solid, long-term basis for our relationship so that sudden eruptions like the painful debate of the last few weeks can be avoided."

The nearly 200 officials and staff members of B'nai B'rith listened attentively and applauded the ambassador, then quizzed him with polite but sometimes tough questions.

"How much of Bitburg was staged for German domestic political propaganda?" asked a board member from Australia.

"The original motivation of the chancellor Helmut Kohl was reconciliation," van Well replied, "reconciliation and the strengthening of the alliance" between West Germany and the United States.

Most questions dealt with how the Federal Republic of Germany is educating German youth on the Holocaust. The ambassador replied that "there can't be any question of trying to keep the memories alive."

In his address, von Well praised B'nai B'rith for an exchange of 30 West German and American Jewish youths scheduled this summer.

He also pointed out that in October, West German President Richard von Weizsaecker will pay a state visit to Israel, the first by a president of the Federal Republic.

"This will be a suitable occasion to solemnly restate our commitment to the Jewish people and to the state of Israel," he said.

He said 350,000 Jews fled Germany in the first six years of Nazi rule and an additional 180,000 were killed. He said today there are 73 Jewish communities in West Germany, with about 30,000 members.

Because there are so few Jews left in Germany, said van Wall, "it is the American Jewry who has become the main torchbearer."