The study examined programming on ABC, CBS, NBC, Fox, WB, PBS, Lifetime, TNT, USA Network and HBO. Sexual content could be anything from discussions about sex to scenes involving intercourse.

Examples of sexual content cited ranged from discussions of sex on the WB's "Gilmore Girls" and "Jack & Bobby" to depictions of oral sex on NBC's "Law and Order: Special Victims Unit" and sexual intercourse on Fox's "The O.C."

The study did not offer an opinion on whether such content is harmful to children. But lead researcher Dale Kunkel said it's generally established that TV influences the behavior of children and teenagers.

"Their sexual knowledge, attitudes, behaviors are all shaped in part by the characters in stories that television conveys," he said.

Kaiser released the study's findings at a news conference with Sen. Barack Obama, D-Ill., followed by a panel discussion with executives from NBC and Fox, Commissioner Kathleen Abernathy of the Federal Communications Commission and others.

"We don't teach our children that healthy relationships involve drunken, naked parties in a hot tub with strangers — but that's what they see when they turn on 'The Real World,' " he said, citing a show on MTV.

"When they're fed a steady diet of these depictions over and over again from the time they're very young, this behavior becomes acceptable — even normal," he said.

Obama said the television industry needs to do more to help parents better navigate the ever-growing number of channels and programs. Making TV ratings easier to understand is one way, he said, adding that that if broadcasters and cable don't do more they are inviting Congress to act.

Tony Vinciquerra, president and chief executive of Fox Networks Group, said parents already have the controls they need on cable and satellite to block channels or programs they deem inappropriate.

Parents with regular over-the-air TV can use the V-chip, technology that's built into televisions and works with an electronically coded rating system to identify programs that contain sex, violence or crude language.

Vinciquerra also said network executives are aware of parents' concerns. "We have debates every minute of every day about what goes on television," he said.

Vicky Rideout, a vice president at Kaiser, said the number of shows that included a message about the risks and responsibilities of sex is very small and has remained flat since 2002.

About 14 percent of the shows with sexual content also had discussions of contraception, waiting to have sex or other safe-sex messages. Although that figure is about the same as it was in the last study, it's up from 9 percent in 1998.

The Henry J. Kaiser Family Foundation is a philanthropic group that studies health care, including reproductive and AIDS-related issues. It is not affiliated with the Kaiser medical organization.

WHAT TEENS WATCH

The top 10 television shows watched by teenagers, according to the Kaiser Family Foundation:

• "American Idol" on Fox

• "The Simpsons" on Fox

• "Desperate Housewives" on ABC

• "Survivor: Palau" on CBS

• "CSI: Crime Scene Investigation" on CBS

• "Extreme Makeover: Home Edition" on ABC

• "The OC" on Fox

• "Family Guy" on Fox

• "Survivor: Vanuatu" on CBS

• "One Tree Hill" on WB