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NEW YORK - It's a question that often prompts a boastful answer or a bashful one: How many sex partners have you had?

Now the U.S. government says it has authoritative statistics, documenting that men are far more likely to play the field than women.

A new nationwide survey, using high-tech methods to solicit candid answers on sexual activity and illegal drug use, finds that 29 percent of American men report having 15 or more female sexual partners in a lifetime, while only 9 percent of women report having sex with 15 or more men.

The median number of lifetime female sexual partners for men was seven; the median number of male partners for women was four.

The survey, released Friday, is based on data collected from 1999 to 2002 for the National Center for Health Statistics, a branch of the Centers for Disease Control and Prevention.

In previous versions of this survey, participants were asked questions in face-to-face interviews. The CDC believes that caused underreporting of behaviors which might be viewed negatively, although the new survey did not provide any comparative results from earlier reports.

This time, data was gathered from 6,237 adults, aged 20 to 59, in what are called computer-assisted self-interviews -- a method designed to provide complete privacy and produce more honest answers.

"This is the first time we've used this technique," said Dr. Kathryn Porter, who served as medical officer for the survey. "The participants have a headset on, they hear questions, they touch the screen with responses. There's no one else in the room and they can take as long as they want."

Porter said the findings would provide grist for further studies, notably on the prevalence and patterns of sexually transmitted diseases.

Though the survey results were presented by the CDC without subjective comment, they will likely provide ammunition to various parties in the ongoing national debate over sex education, cohabitation and access to birth control.

Many of the conservative groups aligned with the Bush administration on social issues promote the goal of sexual abstinence until marriage. The survey found only about 11 percent of never-married adults had remained chaste.

Among the other findings:

• About 96 percent of U.S. adults have had sex.
• Sixteen percent of adults first had sex before age 15, while 15 percent abstained from sex until at least age 21.
• The proportion of adults who first had sex before age 15 was highest for non-Hispanic blacks (28 percent) compared to 14 percent for both Mexican-Americans and non-Hispanic whites.
• Six percent of blacks abstained from sex until age 21 or older, fewer than Mexican-Americans (17 percent) or non-Hispanic whites (15 percent).
• Black men and women were more likely to report having 15 or more partners in a lifetime (46 percent and 13 percent, respectively) than other racial or ethnic groups.
• Seventeen percent of men and 10 percent of women reported having two or more sexual partners in the past year.
• Twenty-five percent of women and 17 percent of men reporting having no more than one partner of the other sex in their lifetime.
• Twenty-six percent of men and 17 percent of women have tried cocaine or other street drugs (not including marijuana) at some time in their life. Seven percent of men and 4 percent of women had done so within the past 12 months.
• Non-Hispanic whites had a higher percentage of ever using cocaine or street drugs (23.5 percent) than blacks (18 percent) or Mexican-Americans (16 percent).
• Adults who were married or had more than a high school education were less likely to use street drugs than others.

The survey, formally titled the National Health and Nutrition Examination Survey, did not include the homeless, prisons inmates or other institutionalized adults.

The questions about numbers of sexual partners specified heterosexual relationships, and thus the survey did not measure the extent of gay or lesbian sexual partnerships. However, Porter said there was no such specificity in the questions about ever having had sex or about the age of first sexual activity, so answers to those could have referred to straight or gay sex.