I'm impressed," said Pauline Cohen proudly, as a Yiddish lullaby played, "how in every time and every place the Jew has made a contribution and fits into the era. In Renaissance Italy, he looks like a Renaissance Italian."

Right behind her in the B'nnai B'rith Klutznick Museum on Rhode Island Avenue NW was visual proof of how Jews adapted to life in Spain, Italy, Greece, Morocco, China and the United States. Cohen, a former teacher, and one of 200 guests at last night's opening of "Among the Nations," added her own oral history, telling a group of friends about a Jewish wedding she happened on in Denmark. "We have an everlasting culture," emphasized Sam Stern, an office interior designer in Chevy Chase.

The exhibit recreates the themes and mood of the Museum of the Diaspora in Tel Aviv, which, in the two years it has been open, has become one of Israel's most popular tourist attractions. "Most of the materials are reproductions, because there are hardly any artifacts of that 2,500 years of Jewish history," explained Miriam Ben-Haim of the Tel Aviv staff as she waled past the slides and photographs depicting circumcision, marriage and death and the cases of ceremonial and religious artifacts.

Philip Klutznick, the secretary of Commerce, who helped plan the Tel Aviv museum and donated the funds for the Washington museum, had spent most of his day "campaigning and champagning" in Connecticut. Greeting old friends was the business of the hour, not any prolonged analysis of the so-called Jewish vote. "I've never had any doubts who will win the election and I think Jews will choose correctly," he said.

Others didn't share the same confidence. Albert Abramson, a local businessman, said, "THE OTHER MORNING i went to breakfast with 12 men and I asked how many of them had decided who to vote for. Ten hadn't decided.And I really haven't made up my mind." Jack Solomon, a slot machine manufacturer, said he was backing Ronald Reagan. "The bureaucracy has gotten too big. I'm supporting Reagan in the hopes that enough people will take a stand and say 'it's enough, get out of our lives,'" he said.