A study of American religious identification shows that the majority of adult adherents continue to be tied to Protestant and other non-Catholic denominations but the numbers of those who say they are non-Christians or have no religion have risen substantially.

The American Religious Identification Survey, 2001, released Monday by the Graduate Center of the City University of New York, is a follow-up to a survey conducted in 1990. It found that 52 percent of American adults are Protestant, 24.5 percent are Catholic and 14.1 percent are not affiliated with a religion. Researchers determined that 1.3 percent of adult Americans described their religion as Jewish and 0.5 percent as Muslim.

The results, based on more than 50,000 adult respondents, found that Protestant and other non-Catholic denominations continue to have the majority of adult adherents--more than 105.4 million--but their proportion dropped from 60 percent in 1990 to 52 percent in 2001.

The number of adults who identify with a non-Christian religion rose dramatically from about 5.8 million to 7.7 million. Their proportion increased slightly--to 3.7 percent from 3.3 percent in 1990.

Researchers found that the number of adults identifying with no religion more than doubled, from 14.3 million (8 percent) in 1990 to 29.4 million (14.1 percent) in 2001.

The number of adults describing their religion as Jewish dropped from 3.1 million to 2.8 million. An additional 2.5 million who said they had no religion or identified with another religion have Jewish parents, were raised Jewish or consider themselves Jewish for some other reason.

Adults who described themselves as Muslim or Islamic totaled 1.1 million, almost double the number in 1990. Twenty-three percent of this group said they were black while the vast majority of the others said they were white or Asian.

The study was released in the same week that the American Jewish Committee announced new research it commissioned that estimates that Muslims of all ages total about 1.8 million, far lower than current estimates reported by some media of 5 million to 8 million. Tom Smith, director of the General Social Survey at the University of Chicago's National Opinion Research Center, said: "It is hard to accept estimates that Muslims are greater than 1 percent of the population, or 2,814,000."

The American Muslim Council responded with an open letter to the committee saying it was disturbed that the Jewish organization "would deny the existence of four and a half million American Muslims."

The CUNY study was directed by Egon Mayer, a sociology professor at the Graduate Center and Brooklyn College, and Barry Kosmin, who directed the 1990 religion study.