It was supposed to be an important moment in American Judaism: the release last week of a $6 million, years-long study of U.S. Jews.

The findings could be critical, shaping how tens of millions of dollars will be spent to keep Judaism alive in the United States at a time when many Jews are marrying outside the faith. Then, just before its scheduled release, the report was withheld.

The 2000 survey's advisers now are in a bitter fight with the nonprofit agency directing the project, and critics are wondering whether the group is trying to bury bad news.

The agency, United Jewish Communities, insists its National Jewish Population Survey is on track and will be made public -- although it won't say when. "There's no smoking gun here," said the agency's president, Stephen Hoffman. "Based upon what I've been told, the study is fundamentally sound."

The survey, which had last been conducted in 1990, tracks key trends, including intermarriage, links to Israel and observance of religious rituals.

The 2000 study was to have been released more than a year ago, but researchers said it was hard to find people willing to participate. The date was pushed back, and speculation grew that the survey was in trouble.

Preliminary results were released last month, including a finding that the U.S. Jewish population had dropped over the past decade from 5.5 million to 5.2 million.

Days before the United Jewish Communities General Assembly in Philadelphia last week, where the remaining results were to be announced, Hoffman said he had learned that "critical data" had been lost and was postponing the release to assess the damage.

Vivian Klaff, one of the top technical advisers, insisted the data were not critical.

Hoffman's action has some critics wondering whether his agency, which raises and distributes millions of dollars for Jewish community work, delayed the release because it did not like the results.

Hoffman denies that. But Barry Kosmin, who led the 1990 study, said United Jewish Communities left itself vulnerable to such assertions by not asking an independent institution to conduct the survey.

"I'm not suggesting any conspiracies," said Kosmin, director of the Institute for Jewish Policy Research in London. "I'm saying if you did it at arm's length, it would be less likely that anyone would say that the leadership would use it to justify what they're doing."