A long-awaited national study has concluded that abstinence-only sex education, a cornerstone of the Bush administration's social agenda, does not keep teenagers from having sex. Neither does it increase or decrease the likelihood that if they do have sex, they will use a condom.

Authorized by Congress in 1997, the study followed 2000 children from elementary or middle school into high school. The children lived in four communities -- two urban, two rural. All of the children received the family life services available in their community, in addition, slightly more than half of them also received abstinence-only education.

By the end of the study, when the average child was just shy of 17, half of both groups had remained abstinent. The sexually active teenagers had sex the first time at about age 15. Less than a quarter of them, in both groups, reported using a condom every time they had sex. More than a third of both groups had two or more partners.

"There's not a lot of good news here for people who pin their hopes on abstinence-only education," said Sarah Brown, executive director of the National Campaign to Prevent Teen Pregnancy, a privately funded organization that monitors sex education programs. "This is the first study with a solid, experimental design, the first with adequate numbers and long-term follow-up, the first to measure behavior and not just intent. On every measure, the effectiveness of the programs was flat."

The report's release comes as questions are being raised in several quarters about abstinence programs. A bill introduced in Congress, sponsored by both Republican and Democratic members, would allocate money for sex education that teaches abstinence and contraception. In addition, eight states that used to receive funding for abstinence programs have decided to stop doing so, two of them very recently. Federal abstinence funds come up for congressional renewal this summer under the Title V grant.

The federal government spends $176 million a year on abstinence-only education, and millions more are spent every year in state and local matching grants. Harry Wilson, a top official in the Department of Health and Human Services, said yesterday that the administration has no intention of changing funding priorities in light of the results.

"This study isn't rigorous enough to show whether or not [abstinence-only] education works," Wilson said.

Some federal money, in addition to state and local dollars, supports comprehensive sex education, he said. What is spent on abstinence "is not that much money when it comes to offering an alternative to the other message." He said modifications in the program are already being considered, including a focus on low-income neighborhoods and extending instruction into high school.

The study did not address the impact of a student's family income on the effectiveness of abstinence-only programs.

The results came as a bit of surprise even to Christopher Trenholm, who supervised the project at Mathematica Policy Research Inc. An early analysis by his organization showed some attitude shifts toward delaying sex among students in the abstinence programs, but those differences disappeared as students got older. One thing they also learned, Trenholm said, was that kids receiving abstinence instruction did not use condoms less often than other kids, a possibility that critics occasionally raise. They also showed slightly better knowledge about the prevention of sexually transmitted disease.

Kids in both groups were knowledgeable about the risks of having sex without using a condom or other form of protection. Knowing that did not mean they put on a condom every time, however. Condom use was not high in either group; of those who had sex, almost half said they used condoms only "sometimes" or "never."

Brown said Mathematica's results underscore what other, smaller studies have shown: "The most effective programs are those that say abstinence is the best choice but birth control and protection are also worth knowing about."

An official at the Sexuality Information and Education Council of the United States agreed.

"Comprehensive education means teaching about abstinence and a myriad of other topics," said spokeswoman Martha Kempner. Among them, she said: "contraception, critical thinking, one's own values and the values of your family and your religious community.

"Abstinence-only was an experiment and it failed."