Among the findings of a sweeping federal government survey of American sexual behavior is one that may surprise those bewailing a permissive and eros-soaked popular culture: More than one-quarter of people interviewed in their late teens and early 20s had never had sex.

And the number was growing.

The latest round of the quaintly named National Survey of Family Growth found that among 15-to-24-year-olds, 29 percent of females and 27 percent of males reported no sexual contact with another person ever - up from the 22 percent of both sexes when the survey was last conducted in 2002.

"The public's general perception is that when it comes to young people and sex, the news is bad and likely to get worse," said Bill Albert, chief program officer of the National Campaign to Prevent Teen and Unplanned Pregnancy, an advocacy organization in Washington.

The seventh and latest round of the survey, first done in 1973, provides a corrective to that view.

"Many, many young people have been very receptive to the message of delaying sexual activity," Albert said. "There's no doubt about it." He added that the nearly 40 percent reduction in teen pregnancy since the 1990s - which experts attribute to both increased condom use and increased abstinence - represents "extraordinary progress on a social issue that many once considered intractable."

The uptick in abstinence is one of many revealing facts arising from structured interviews with a random sample of 13,495 Americans, ages 15 to 44, that were done from 2006 to 2008. The findings provide evidence for almost every theory and supposition about the nation's secret sex life.

The survey results, released Thursday, suggest that oral sex may be a gateway to vaginal sex but that for some teens it is a stopping point. Most adults are monogamous. About 4 in 10 adults have had anal sex. Women are more likely than men to have same-sex liaisons. Or at least are more comfortable talking about them.

Conducted by the Department of Health and Human Services, the survey provides basic information for public health policymakers concerned with such issues as sexually transmitted disease. There is no single fact that it is trying to ferret out or message that its 49 pages of text and tables seek to deliver.

But Anjani Chandra, the demographer who is the lead author of the report, said that "for some people, it may be news that these behaviors exist at all in the general population."

When first run, the survey queried only married and formerly married women. Single women and then men were later included, as were more detailed questions about sexual practices.

Parts of the survey are now so explicit that even though the interviewer and subject are face to face, some questions are asked and answered using a computer screen so that the answers are completely private.