Two in every three young Americans have engaged in oral sex, about the same percentage as those who have engaged in vaginal intercourse, the study by the Center for Disease Control and Prevention's Center for Vital Statistics found.

It also showed that the rates of both practices among the U.S. youth have dropped since a decade ago.

The study showed that about equal numbers of young women and men aged between 15-24 have had oral sex, and that about a quarter - 26 percent of women and 24 percent of men - had first had oral sex before engaging in vaginal intercourse.

Around a quarter of youth had likewise had oral sex only after first experiencing vaginal intercourse, the study said.

The belief that oral sex was being practiced more and vaginal sex less to avoid pregnancy and STDs has gained traction in recent years.

"Now we know that's not necessarily true," Monica Rodriguez, president and chief executive of the nonprofit group, the Sexuality Information and Education Council of the United States, told Reuters.

"Now we have some real data," she said after reviewing the new study based on 6,346 interviews conducted between 2007-2010.

LESS SEX

Teenage oral sex has declined slightly since 2002, as has vaginal sex, the author of the CDC study Casey Copen said. She attributed the drop to a "decreasing trend in sexual experience among teens."

The study also revealed differences in experiences linked to race, education and income.

White youth and those from more educated, two-parent homes are more likely than others their age to engage in oral sex first, the study showed. It found that 44 percent of white youth had oral sex before vaginal sex, compared to 30 percent of black youth.

"A higher percentage of females and males who had oral sex, but not yet had vaginal intercourse, had mothers who had some college education or higher," the study found.

Also, females who had oral sex, but had not yet had vaginal intercourse, were more likely than others their age to live with two biological parents, according to the study.

(Editing by Cynthia Johnston)

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