NEW YORK, Feb. 2 (JTA) — How many Orthodox Jews are there in America today? No one knows for sure, since it has been nearly a decade since the 1990 National Jewish Population Study and the 1990 United States Census were conducted. When the National Jewish Population Study, sponsored by the Council of Jewish Federations, was published, many Orthodox Jews involved in communal affairs complained that it underrepresented their community. But together the two studies remain, to date, the most reliable information about the percentage of American Jews who identify as Orthodox. Questions of religion are not asked in the U.S. census, but other identifying questions are — such as if Yiddish is the first language spoken in the home, which would, today, be a likely indicator that its residents are fervently Orthodox, or haredi. The NJPS found that just more than 7 percent of American Jews — or a maximum of 470,000 — were Orthodox. Orthodoxy, more than any of the other movements, has lost adherents in the last generation, said Samuel Heilman, a professor of Jewish studies and sociology at the City University of New York. “People who in the past might have called themselves Orthodox don’t do so now, because the demands of being Orthodox are greater,” said Heilman. In the past, Heilman believes, self-defined Orthodox Jews would have included those who belonged to an Orthodox synagogue but did not often attend it, who would not have sent their kids to day school or who would not have eaten only kosher food. Today, he said, “the ante has been raised” in the Orthodox community and those who identify as such are expected to be more observant. Determining which of the 470,000 Orthodox Jews in America are modern, or centrist, Orthodox is tricky, Heilman said. “The question of how you define someone as haredi is not always consistent,” he said, using the term for fervently Orthodox. “A person can be centrist during the week and haredi on the weekend if on Saturday he puts on a black hat and looks and thinks differently,” Heilman said. Still, by analyzing the census and NJPS, Heilman found that roughly 40 percent of American Orthodox Jews today — or about 200,000 — are haredi, while 60 percent are modern, or centrist, Orthodox. The haredi proportion is “much higher than we thought,” Heilman said, and is largely attributable to the significantly higher birthrate among haredi Jews than among the centrists. Haredi families often have between eight and 12 children, with some producing as many as 20. Centrist Orthodox families tend to produce between three and five offspring, he said. Heilman said that he expects the next National Jewish Population Study, to be conducted in 2000, to find the number of Orthodox Jews remaining stable or growing just slightly as a percentage of American Jewry overall.