Increasing number of Jews marrying outside the faith could be a major factor, the study by Pew Research Center suggested.
American Jews, however, overwhelmingly said they are proud to be Jewish and have a strong sense of belonging to the community. About 94 per cent said they are proud to be Jewish.
About 22 per cent of 3,475 people the survey interviewed said they have no religion.
Secularism has a long tradition in Jewish life in the US, and most Jews in America seem to recognise this: 62 per cent say being Jewish is mainly a matter of ancestry and culture while 15 per cent say it is mainly a matter of religion.
According to the study, intermarriage rates have risen among Jews with nearly 6-in-10 respondents who married after 2000 having a non-Jewish spouse, as compared to 4-in-10 who were married after 1980.
The Jews who intermarried were also less likely to raise their children as Jewish by religion, found the study released today.
In stark contrast, the survey found two-thirds of Jews of no religion say they are not raising their children Jewish or partially Jewish - either by religion or aside from religion.
Release of the findings coincided with a visit to the US by Israeli Prime Minister Benjamin Netanyahu.
