WASHINGTON - After falling steadily for more than a decade, the birth rate for American teenagers jumped last year for the first time since 1991, federal health officials reported Wednesday, a sharp reversal in what has been one of the nation's most celebrated social and public health successes.

The birth rate rose by 3 percent between 2005 and 2006 among 15- to 19-year-old females, after plummeting 34 percent between 1991 and 2005, the National Center for Health Statistics reported.

"This is concerning," said Stephanie Ventura, who heads the center's reproductive statistics branch. "It represents an interruption of 14 years of steady decline. Now, unexpectedly, we have an increase of 3 percent, which is a significant increase."

Ventura said it is too soon to know whether the increase was the beginning of a trend or an aberration. But she said the magnitude of the rise, especially after many years of decline, is worrisome.

"This early warning should put people on alert to look at the programs that are being used to see what works," Ventura said.

The new data reignited debate about abstinence-only sex-education programs, which receive about $176 million a year in federal funding. Congress is debating whether to increase that by $28 million.

"The United States is facing a teen pregnancy health-care crisis, and the national policy of abstinence-only programs just isn't working," said Cecile Richard, president of the Planned Parenthood Federation of America.

But proponents of abstinence education defended the programs, blaming the rise on the ineffectiveness of conventional sexual education programs that focus on condom use and other contraceptives, as well as the pervasive depiction of sexuality in the culture.

"This shows that the contraceptive message that kids are getting is failing," said Leslee Unruh of the Abstinence Clearinghouse.

Other experts said many factors could be playing a role. It could be, for example, that complacency has set in, or that the increase reflects of a broader trend cutting across all ages. Birth rates have also increased for women in their 20s, 30s and early 40s.

The teen birth rate rose sharply between 1986 and 1991, when it hit an all-time high of 61.8 births per 1,000 girls. The increase led to a massive campaign to counter the trend, and the rates of both teenage sexual activity and teen births began falling steadily every year.

Advocates noted that despite the 14-year decline that preceded last year's rise, U.S. teens are still far more likely to get pregnant and have children than those in other developed countries, and teenage mothers and their children are far more likely to live in poverty.

"The vast majority of teenage mothers never finish high school," said Sarah Brown of the National Campaign to Prevent Teen and Unplanned Pregnancy. "Teen pregnancy and child care is directly related to poverty, both for the mother and the child. This should be a wake-up call for a renewed focus on preventing teen pregnancy."

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