Nearly half the Jews who will marry in the United States this year will wed non-Jewish partners. In some European countries, three-quarters of such marriages include non-Jewish partner.

These conclusions of the Commission of synagogue relations of the Federation of Jewish Philanthropies were reported recently by its director, Rabbi Isaac Trainin.

But, there are (traditionalist) trends going on in American Jewish society that could bring down the number of mixed marriages in the next 25 years, Rabbi Trainin said. "This would not be so for Europe," He continued in a telephone interview from his New York office.

The projected figure for this year is based on an original study for the federation compiled two years ago by the Council of Jewish Federations and Welfare Funds.

The federation has continued to use the scientific base established by the study, and results are further corroborated by the "close tabs we keep on who Jews by our task force of mixed marriage," said Rabbi Trainin. The marriages are reported to the federation through what he called a national network of rabbis and Jewish organizations." The task force was established in 1960.

"In the U.S. Jewish community there has been a steady increase in the number of mixed marriages for the last 25 years," Rabbi Trainin said.

"This is largely a result of the parallel phenomena of acculturation and assimilation.

"More simply put, mixed marriages are the result of a Jewish minority living in a gentile world," he said. Jews marrying non-Jews is "one inevitable result of living in an open and free society rather than a separatist one." he continued.

"The European information we have was gathered through the years from Jewish community leaders in Scandanavia, Holland, Germany and France," he said.

"It's much easier (to gather information about Jews) in those countries," said Rabbi Trainin. "Jewish communities there are much more tightly organized."

No survey was made in Great Britain.

The federation estimated that if figures could be obtained on Jews marrying in the Soviet Union, the figure on mixed marriages would be very high. "We do know that quite a number of the Jews who were let out of Russia to go to Israel were married to non-Jews," the rabbi said.

Rabbi Trainin said that there are no signs that the number of European Jews with non-Jewish spouses will decrease. "The chances of young Jewish people meeting each other are minimal because there are very few (Jewish) communities left in Europe that are strong and unified.

"In Mid-Eastern countries (excluding Israel) those Jews left are very traditional, very religious," he said.

"They don't want to marry Arabs or other non-Jews."

In the United States, the phenomenon of "neotraditionalism" among some American Jews could discourage intermarriage enough to reverse the current trend, according to Rabbi Trainin.

"Neotraditionalism among Jews is similar to neofundamentalism among Christians," he said. "It's becoming more accelerated."

"More and more young people here are becoming very religious . . . 25 years ago, there weren't more than five college campuses where a Jew could get kosher food. Now, there are more than 100 such campuses. There are more Jewish day schools, and from these you are getting more traditional Jews," he said.