NEW YORK - More than nine out of 10 Americans, men and women alike, have had premarital sex, according to a new study. The high rates extend even to women born in the 1940s, challenging perceptions that people were more chaste in the past.

"This is reality-check research," said the study's author, Lawrence Finer. "Premarital sex is normal behavior for the vast majority of Americans, and has been for decades."

Finer is a research director at the Guttmacher Institute, a private New York-based think tank that studies sexual and reproductive issues and which disagrees with government-funded programs that rely primarily on abstinence-only teachings. The study, released Tuesday, appears in the new issue of Public Health Reports.

However, Janice Crouse of Concerned Women for America, a conservative group which strongly supports abstinence-only education, said she was skeptical of the findings.

"Any time I see numbers that high, I'm a little suspicious," she said.

The study, examining how sexual behavior before marriage has changed over time, was based on interviews conducted with more than 38,000 people - about 33,000 of them women - in 1982, 1988, 1995 and 2002 for the federal National Survey of Family Growth. According to Finer's analysis, 99 percent of the respondents had had sex by age 44, and 95 percent had done so before marriage.

Even among a subgroup of those who abstained from sex until at least age 20, four-fifths had had premarital sex by age 44, the study found.

Finer said the likelihood of Americans having sex before marriage has remained stable since the 1950s, though people now wait longer to get married and thus are sexually active as singles for extensive periods.

The study found women virtually as likely as men to engage in premarital sex, even those born decades ago. Among women born between 1950 and 1978, at least 91 percent had had premarital sex by age 30, he said, while among those born in the 1940s, 88 percent had done so by age 44.

"The data clearly show that the majority of older teens and adults have already had sex before marriage, which calls into question the federal government's funding of abstinence-only-until-marriage programs for 12- to 29-year-olds," Finer said.

Under the Bush administration, such programs have received hundreds of millions of dollars in federal funding.

"It would be more effective," Finer said, "to provide young people with the skills and information they need to be safe once they become sexually active - which nearly everyone eventually will."