NEW YORK — The Orthodox movement claims the lion's share of synagogues in the United States, despite being the smallest of the three major branches, according to a new census by the American Jewish Committee.

Of 3,727 synagogues in the United States, 40 percent are Orthodox, 26 percent Reform and 23 percent Conservative, according to the census, the first to count U.S. synagogues since 1936.

Other groups, including Reconstructionist, Sephardi, traditional, humanistic and gay-lesbian, each make up 3 percent or less of all synagogues, according to the census.

The study, by Jim Schwartz, Jeffrey Scheckner and Laurence Kotler-Berkowitz, does not try to count synagogue membership, which Schwartz called "a very tricky" area that is difficult to define.

Yet the study offers the most detailed tabulation of U.S. synagogues in decades. The researchers cross-referenced the movements' synagogue lists with Jewish directories, phone books, phone surveys and other data to compile the first such report since the 1936 Census of Religious Bodies survey.

That U.S. government study counted 3,728 "congregations," though this study's authors said it remains unclear how many of those were housed in synagogue buildings.

Of the Orthodox synagogues, 36 percent were not officially tied to any organization, 23.5 percent belonged to the Orthodox Union, 23.1 percent to Chabad/Lubavitch, 10 percent to the National Council of Young Israel, 4 percent to the fervently religious Agudath Israel of America and 6.5 percent to Sephardic organizations.

With the Orthodox movements representing only 8 to 10 percent of American Jews, according to surveys, it's a matter of debate why they have built so many synagogues.

"It's true there's been an Orthodox resurgence, but the number of Orthodox synagogues has always been larger than their proportion of the population," said Lawrence Grossman, editor of the AJCommittee's American Jewish Year Book, which will carry the full study in its 2002 edition.

"Any time you get 10" Orthodox "people together, they'll break off and form their own minyan," he added.

Rabbi Avi Shafran, a spokesman for Agudath Israel, agreed that many Orthodox shuls have only 20 or 30 members, compared with some 200 to 300 members or more in many Conservative and Reform synagogues.

Orthodox Jews take very seriously the nusach, or liturgical style, of their shul's prayers, according to traditions usually based on family habits, he said.

"We tend to be very religious about our observance," he said. "When you live in a shul instead of visiting it once or twice a week, you want to feel comfortable there."

Some disputed his analysis.

Rabbi Jerome Epstein, executive vice president of the United Synagogue of Conservative Judaism, said Orthodox congregations are largely "neighborhood" congregations because members don't drive on Shabbat.

"The real issue is the riding issue," he said. "It's not that the Orthodox take services more seriously."

In many large Conservative and Reform synagogues, he added, members also follow "different styles of prayer," but they form their own minyanim to accommodate their preferences, rather than entirely new shuls.

Rabbi Eric Yoffie, president of the Reform movement's Union of American Hebrew Congregations, said the number of synagogues "doesn't really mean anything."

He will look more seriously at the upcoming National Jewish Population Survey, which should show how many Jews belong to each denomination, Yoffie said.

The AJCommittee study "is useful information, as long as one doesn't draw inappropriate conclusions from it," he said.

Trying to avoid a dispute over "What is a synagogue?" the census defined one as a place whose primary purpose is religious; that features a permanent physical location for prayer; where services are scheduled regularly; that is led by a rabbi, cantor or lay leader; and that is considered a synagogue by its members.

Meanwhile, Schwartz said this census affirmed some long-held assumptions about synagogues in the United States:

*The 50 metropolitan areas with the largest Jewish populations contain 82 percent of all synagogues.

*Within the 50 areas with the densest Jewish populations, seven metro areas contain more than 100 synagogues, or 58 percent of all synagogues in the country.

*The New York-northern New Jersey-Long Island area, which has the heaviest Jewish population in the United States, contains one-third of all U.S. synagogues. Next came the Los Angeles-Riverside-Orange County area, with 7 percent, and Boston-Worcester-Lawrence, with 5 percent.

*New York has the most synagogues, with 995, followed by 425 in California, 331 in New Jersey, 263 in Florida and 201 in Massachusetts. These five states also have the largest Jewish populations — except for Pennsylvania, which has slightly more Jews than Massachusetts but four fewer synagogues.

One fact seemed beyond dispute: Overall, the study showed that American Jews are "primarily an urban population," Schwartz said.

But since the study did not attempt to analyze what the synagogue numbers mean for the relative strength of each movement, the census is likely to spark even further debate.