WASHINGTON — Sexually speaking, Americans are mixing it up a good deal more than they have in the past.

The first comprehensive snapshot of Americans’ sexual activity in almost two decades suggests a social landscape changed by the HIV/AIDS virus and by an increasingly open national conversation about sexual acts other than plain-old intercourse.

Across the lifespan — although less early than popular culture might have us believe — Americans report they are masturbating, alone or with a partner, engaging in oral sex and experimenting with same-gender sex more often than they owned up to in the 1980s, according to a study released Monday.

“”The sexual repertoire of Americans has sort of expanded,”” said Michael Reece, director of Indiana University’s Center for Sexual Health Promotion and a leading author of the National Survey of Sexual Health and Behavior, published Monday in a special issue of the Journal of Sexual Medicine. Though vaginal intercourse is hardly on its way out, the practice has declined as other sexual acts have gained traction.

“”We’ve always looked at these other sexual activities as foreplay, with the notion that ‘That’s not really sex,'”” Reece said. But amid a din of messages selling safe sex, pregnancy prevention, female empowerment and sexual pleasure, acts once seen as the starter course have not only become an essential ingredient in our sexual diet: They are frequently the main course.

The result is a sexual smorgasbord that by all appearances has become more satisfying to women. Though men were more likely to report orgasm during vaginal intercourse, women told researchers they were more likely to have orgasms from a variety of sex acts, including oral sex and vaginal intercourse.

The survey suggested some ongoing miscommunication between the sexes when it comes to satisfaction. All told, 64 percent of women reported having achieved orgasm in the course of their most recent sexual “”event.”” A higher proportion of men — 85 percent — reported that their partner had experienced orgasm during their most recent sexual encounter.

Though a small fraction of those men may have been having sex with other men, that explanation could not account for a 21-point gap between men’s and women’s accounts, researchers said.

Former Surgeon General M. Joycelyn Elders, in an accompanying editorial, said the findings would help our “”sexually dysfunctional society”” address sex as a positive source of pleasure and health. In a country where 30 percent of health care spending is related to sexuality, she wrote that the national conversation about sex must shift from its focus “”only as prevention of pregnancy and disease to a discussion about pleasure.””

In all, 5,865 U.S. residents answered the survey, which was the first ever to gather data on sexual activity from Americans at far ends of the age spectrum. The last such survey, conducted by the same researchers in 1992, queried people between the ages of 18 and 59 about their sexual activities. In contrast, the current study asked adolescents as young as 14 and adults as old as 94 whether and what kind of sex they were having.

The study showed that, despite the widespread concern about early-adolescent “”hook-ups,”” “”sexting”” and “”friends with benefits,”” young teenagers are largely not having sex with anyone but themselves. Among 14- and 15-year-olds, roughly one in 10 said they were having sex with a partner. But 62 percent of boys and 40 percent of girls in this age group reported they had masturbated by themselves in the past year.

Men and women over the age of 60 continued to be sexually active and adventurous in large numbers, with 38 percent of men and 25 percent of women ages 60-69 reporting that they had received oral sex from a member of the opposite sex in the past year. Those number declined to 19 percent and 8 percent for men and women, respectively, in their 70s and beyond.

Not surprisingly, given the fact the study was underwritten by the condom-manufacturer Trojan, condom use was a major focus of the survey. The survey found condom use is widespread among the sexually active: One in four acts of vaginal intercourse involved a condom, a number that rose to one in three among partners who were not cohabitating.