* Rates of sex among teens, young adults declines
* Some STDs on the rise, especially among teens
* More young women say having sex with each other
WASHINGTON, March 3 (Reuters) - The number of U.S. teenagers and young adults who say they are abstaining from sex is on the rise, even as more young women report having sexual contact with each other, U.S. government researchers said on Thursday.
The U.S. Centers for Disease Control and Prevention (CDC) said in 2006-2008, 29 percent of women and 27 percent of men ages 15 to 24 reported not having any sexual contact compared with 22 percent in 2002.
At the same time, the CDC's National Center for Health Statistics found a growing number of young women who said they have had some form of sex with another woman, rising to 13 percent in the latest survey, from about 12 percent in the 2002 survey.
The number of young men reporting same-sex encounters fell from 5 percent to 4 percent over the same time period.
It also showed an overall increase in reports of the sexually transmitted disease chlamydia, especially among 15 to 19-year-olds. The bacterial infection is the most common STD in the United States and can lead to complications if untreated. Some people have no symptoms, making it easier to spread.
The CDC report aims to provide data to help health officials prevent the spread of sexually transmitted diseases and unplanned pregnancies nationwide.
Its findings for 2006 to 2008 are based on interviews with about 13,500 men and women ages 15 to 44. Overall, it found few changes in the nation's sexual patterns compared to CDC's last survey in 2002.
Among teens, however, the center this time tried to take a closer look at certain, specific sexual behaviors that youth may not typically report as sex because it is not traditional vaginal intercourse.
"This focused look at oral and anal sex among teens and young adults is prompted by concerns that some young people may engage in other types of sexual contact before they have vaginal intercourse, to avoid the risk of pregnancy," researchers said.
"In addition to placing themselves at risk of STIs (sexually transmitted infections), some studies have documented that engaging in these other types of sexual contact may hasten young people's initiation of vaginal intercourse," they added.
Of youth aged 15 to 24 who said they have had sex, nearly 63 percent of women and 64 percent of men had oral sex compared to nearly 69 percent in 2002.
About 21 percent of young men said they have had anal sex, compared to nearly 22 percent in 2002, while the number of young women having anal sex was unchanged at about 20 percent. (Reporting by Susan Heavey; Editing by Julie Steenhuysen and John Whitesides)