The first major survey of American Jews in more than 10 years finds a significant rise in those who are not religious, marry outside the faith and are not raising their children Jewish — resulting in rapid assimilation that is sweeping through every branch of Judaism except the Orthodox.

The intermarriage rate, a bellwether statistic, has reached a high of 58 percent for all Jews, and 71 percent for non-Orthodox Jews — a huge change from before 1970 when only 17 percent of Jews married outside the faith. Two-thirds of Jews do not belong to a synagogue, one-fourth do not believe in God and one-third had a Christmas tree in their home last year.

“It’s a very grim portrait of the health of the American Jewish population in terms of their Jewish identification,” said Jack Wertheimer, a professor of American Jewish history at the Jewish Theological Seminary, in New York.

The survey, by the Pew Research Center’s Religion & Public Life Project, found that despite the declines in religious identity and participation, American Jews say they are proud to be Jewish and have a “strong sense of belonging to the Jewish people.”