There is no good scientific evidence that teaching abstinence to teenagers will by itself prevent unwanted pregnancies and sexually transmitted diseases, say the authors of a recent study. Yet they found that comprehensive sex education is declining and that more youngsters are being taught nothing more than abstinence.

As with similar debates over stem cell research and abortion, California and the Bush administration are at loggerheads over an ethical issue with far-reaching public consequences -- in this case, the best approach to sex ed for middle and high school students.

More than $1 billion in federal aid has been poured into state-run abstinence-only programs in the past decade after the Bush administration decided there was an imbalance that favored comprehensive sex education and slighted abstinence. State school systems accepting the federal money are required to teach that sexual activity outside marriage is likely to have harmful psychological and physical effects, and that a married, monogamous relationship is the expected standard.

California is one of only three states -- the others are Maine and Pennsylvania -- to refuse the federal education funding tied to abstinence.

The recent study, by a team of scholars at the Guttmacher Institute in New York headed by Laura Duberstein Lindberg, looked at instruction between 1995 and 2002 nationwide and found that "teenagers were significantly more likely to have received instruction about how to say no to sex than ... birth control methods" and that abstinence was being pushed in sex ed classes "in the absence of any substantial scientific evidence supporting the effectiveness of the approach."

Published in the December issue of Perspectives on Sexual and Reproductive Health, a leading journal, the article attributed the trend to the federal funding, which since 1996 "has shifted toward programs that teach only abstinence and restrict other information."

Under an education code revision passed in 2003, teachers in California school districts are required to teach HIV/AIDS prevention and are also permitted to teach comprehensive sex education, as virtually all districts do. But exactly what districts teach is up to them, so long as they adhere to state guidelines requiring that their information be medically accurate and that they provide information about contraception while emphasizing that abstinence is the only sure method to avoid pregnancy.

California "made it clear where we stand," said Hilary McLean, press secretary for state schools chief Jack O'Connell. "And yet the Bush administration and the state are still debating this."

Douglas Kirby, a senior researcher at ETR Associates in Scotts Valley (Santa Cruz County) and the author of a far-reaching 2005 survey of the effectiveness of sex education programs worldwide, said that the Guttmacher Institute conclusion was "not surprising" but was "very disturbing. We've put more than $1 billion into abstinence-only (education) when we do not know whether these programs work," he said.

Among the 83 studies on the effectiveness of various sex education programs that Kirby reviewed, he found six studies of abstinence-only programs that met his research standards. "While that was too few to reach any conclusions," he wrote, none of the six programs delayed the age at which the students first had sex.

"The jury is still out," Kirby said in an interview. "At the same time, abstinence-only programs are replacing programs where we have good evidence that they do work."

The debate -- as much cultural and political as it is scientific -- over the most effective way to help young people avoid early sexual activity, pregnancy, abortion and sexually transmitted diseases, and their economic and societal consequences, is taking place amid trends that indicate the sexual practices of teens are changing.

Since 1991, teen pregnancies in the United States have declined by one-third, according to the Centers for Disease Control and Prevention. Researchers at the CDC also have found that 46.8 percent of high school students say they have had intercourse, a 13 percent decline over that same period.

Another recent survey by the Guttmacher Institute revealed that 95 percent of Americans say they had premarital sex.

"If people were to remain abstinent until marriage," Kirby said, "then we would in fact dramatically reduce unintended pregnancy, sexually transmitted disease and poverty.

"On the other hand, we know that people in this country greatly value sexual intimacy regardless if it's in marriage. So it's not accurate to say that abstinence is the value of the United States when it's not held by 95 percent of the population."

Angela Griffiths, executive director of Await & Find, a Hayward-based abstinence-only program, said refusing federal aid is costing California more than $7 million a year. The loss of an opportunity to reach more youngsters "makes me want to puke," she said.

Community-based programs in California do receive abstinence-only funds from a separate federal funding stream established in 2000. Await & Find gets $800,000 a year in Community-Based Abstinence Education Program funding -- the highest amount awarded to any California nonprofit.

Griffiths also took issue with the Guttmacher Institute's conclusion that there is no proof that abstinence-only programs are effective.

"That's incorrect," she said. "Mind you, it depends on how you define abstinence. If you walk into a classroom and just say, 'Don't have sex,' that is narrow, fear-based and inappropriate. We provide comprehensive primary health education that helps young people abstain from any behavior that is potentially harmful," including eating disorders, drug use and violence, as well as sex.

Kirby said that one tactic of the Bush administration was to eliminate a list of programs that were proven to work, compiled by the CDC. Those programs take a multitude of approaches, but have many characteristics in common. "It was eliminated because it had no abstinence-only curricula," Kirby said. "It was very sad, a huge loss. The political pressure in this field has been astounding."

In November, the Bush administration appointed a new abstinence-friendly chief of family planning at the Department of Health and Human Services. Dr. Eric Keroack had been medical director at a Massachusetts pregnancy counseling organization whose Web site states: "The crass commercialization and distribution of birth control is demeaning to women, degrading of human sexuality, and adverse to human health and happiness."

The administration also has budgeted another $241.5 million for abstinence-only programs in 2007. Kirby compared California and Texas, two states he said were similarly populous and were home to many Hispanics, a group whose teen pregnancy rates are high.

"California took a very progressive approach," he said. "Texas pushed abstinence and made it a little more difficult for teens to receive contraceptives. Pregnancy did go down between 1991 and 2004, but Texas had the second-lowest decline of all states, 19 percent. California had the second-greatest decrease, 46 percent.

"What's really sad is that Bush is trying to take some of the policies that didn't work in Texas and implement them nationwide."

"Wonderful as California is," said Claire Brindis, a professor of pediatrics and health policy at UCSF, "adults have jumped to the conclusion that we have enough solid family life education."

She believes comprehensive sex education should be required, rather than merely permitted, by the state. "Because there are so many myths out there," Brindis said, and teens grow up in a culture dense with sexualized mass media.

"One myth I've heard is that a person can't get pregnant the first time, and by the way, 20 percent of teens do. I've heard that if your boyfriend drinks Mountain Dew you won't get pregnant, or if you have sex standing up. Or if you sit on a cold sidewalk after you have sex -- I heard that in Southern California.

"I see in my work how early childbearing is both a result of poverty and how it contributes to an endless cycle of poverty. There's a lot of people who believe knowledge is dangerous, that if you give kids more information about condoms they'll go out and have sex.

"But isn't it better," Brindis asked, "to give young people and our large immigrant population the tools to plan? I can't think of anything more moral."