BY KAT GLASS

If it weren't for Hispanic births, the United States could be confronting long-term population declines similar to those in Germany, Japan and other industrialized countries.

Hispanics are the only ethnic group now producing more than two children per family, according to a Census Bureau report released Monday. That's the number necessary to replace the mother and father and keep the population stable.

''The Hispanic population is growing; whites and Asians are not replacing themselves,'' said Jane Dye, the Census Bureau demographer who wrote the study. The average U.S. woman produces 1.9 children, but broken down by ethnicity, the numbers are 1.7 for Asian Americans, 1.8 for non-Hispanic whites, 2.0 for blacks and 2.3 for Hispanics. Native Americans weren't included in the report. The fertility rates are sufficient, combined with immigration, to keep the U.S. population growing.

''It's the Hispanic population that is keeping us above water in terms of growth, in terms of births,'' said William Frey, a demographer for The Brookings Institution, a center-left policy research organization in Washington.

A CLOSER LOOK

The report took a closer look at women who gave birth between January 2005 and December 2006. It found that: About a fifth of women at the end of childbearing age -- 40 through 44 years old -- have no children, double what the childless rate was 30 years ago. This figure approaches the rates during the Great Depression, according to Andrew Cherlin, a sociology professor at Johns Hopkins University who focuses on families and public policy. About a third of women with newborns didn't have husbands at home.

''A half-century ago, a woman who had a child outside of marriage was highly stigmatized,'' Cherlin said. ``Now, she's likely to be accepted.''

Women, who overall are more educated than ever, are waiting longer to have children. Mothers with at least a bachelor's degree have the most children when they're 30 to 34. For women who don't finish high school, that peak occurs when they're 20 through 24.

LOWEST IN NORTHEAST

Women in the Northeast have the lowest fertility rates, while women in the Midwest have the highest, the report said. Utah was the most fertile state, with 83.2 births per 1,000 women in the year studied.

The high birthrates of Hispanic women should make policymakers reorder their spending, Frey said.

``We need to focus a lot more than we have before on the education opportunities for immigrant children. This makes very clear that they're a big part of our future.''

To census researcher Dye's surprise, Hispanic birthrates didn't fall consistently as the ethnic group assimilated into U.S. society. Instead, they dropped in the second generation but rose in the third.

''I wondered why that was true, and found that those second-generation Hispanic mothers did have higher education attainment than the third generation,'' Dye said.

Falling birthrates have one advantage, according to demographic experts: They ease pressure on scarce natural resources. But there's a downside, Cherlin said.

``It means that 25 years from now, there'll be many elderly people who are childless and who may not have anybody to care for them.''