When the nation's Orthodox rabbis gathered here this week for their annual midwinter conference, they spent one day of their three-day session on Capitol Hill making sure members of Congress were up to date on the convictions of American Jews on the Middle East.

"Israel -- that is one thing the American Jewish community is united on," explained Rabbi Bernard Rosensweig, 52, of Kew Gardens, N.Y., president of the Rabbinical council of America, the Orthodox rabbinical body.

American Jews, he went on, are united in their concern that America "not be partisan on one side, for Egypt," in peace negotiations, in their concern for the future safety of Jews in Iran, in their outrage at Ambassador Andrew Young's overtures toward representatives of the Palestine Liberation Organization.

In other areas, however, there are sharp differences in the American Jewish community.

While most other Jewish groups have endorsed the Equal Rights Amendment, for instance, the Orthodox do not.

Orthodox Judaism, Rosensweig explained, holds that a woman "has total equality before the law and the same heavenly rewards await both sexes." But he expressed the fear that ERA "may be implemented in ways which collide with the moral and religious ideals to which we are all committed."

He speculated that under ERA, women might be drafted not only into the army but into coed barracks as well; that universities might be compelled to make all dormitories coed. "Have not the courts recently affirmed the rights of female reporters to go into men's locker rooms and the rights of girls to play on boys' teams?" he asked.

Rosensweigh pointe out that the primary problem faced by every branch of Judaism today is Jewish survival. The combined effects of assimilation -- "people opting out of Judaism... not even entering into another tradition" plus a declining birthrate among Jews has produced an "explosive situation," he said.

"The population explosion may be a problem to the people in India, but to the Jews, who haven't made up the 6 million" who were slaughtered in World War II "it's the last thing we need," he said.

While he took some comfort in the fact that the birthrate among the Orthodox is higher than in other branches of Judaism, he added that "Jews overall have a lower reproductive rate than the American average."

Rosensweig, in an interview at Congregation Beth Sholom here, where the convocation was held, characterized Orthodox Judaism as "the last to mature in this country... in language, in education... we are a new generation. An English-speaking Orthodox rabbinate is relatively new on fortunately grown" among the Orthodox.

But the Americanization and education of Jews also has been costly in terms of young people. With their greater exposure to the non-Jewish world, large numbers are lost to the faith through intermarriage, which Rosensweig admitted, "has also unfortunatley grown."

"Every mixed marriage is a knife in the heart of Judaism," said Rosensweig. It presents particularly poignant problems to Orthodoxy.

On the one hand, the rabbi explained, "We are not ready to give up on any Jew... a Jew is a Jew is a Jew." But at the same tiem, a Jew who marries outside his faith is barred from membership in most Orthodox synagogues, he said.

Orthodoxy is the smallest of the religious divisions of Judaism in this country, accounting for a little over 10 percent of all American Jews, according to the American Jewish Yearbook. Orthodoxy insists on the strictest and most traditional adherence to the halakha, the Jewish code of law that governs both secular and religious aspects of life.

Rosensweig, a native of Canada, was sharply critical of a program launched last month by Reform Judaism to seek converts, particularly among non-Jewish partners lin mixed marriages.

"It's not acceptable," the New York rabbi said of the effort. "The thrust of that proposal is an admission of failure... a prophecy of doom. It says that unless we move out from Jewish groups, we will not survive."

Rosensweig maintains that Orthodoxy has "had better success" than other branches of Judaism in attracting the nonreligious, secularized young Jews, particularly those on college campuses. "The young people want something that is authentic, genuine," he said.

"There is a disillusionment on the part of many young people," said the rabbi, who teaches courses in Jewish history at Queens College in New York. "Many young people are looking for a genuine Jewish expression -- not a cross (of Judaism) with Protestantism."