WASHINGTON - Melting pot or racial divide? The growth of interracial marriages is slowing among U.S.-born Hispanics and Asians. Still, blacks are substantially more likely than before to marry whites.

The number of interracial marriages in this country has risen 20 percent since 2000 to 4.5 million, according to an analysis of census figures. That is a marked drop-off from the 65 percent increase between 1990 and 2000.

About 8 percent of U.S. marriages are mixed-race, up from nearly 7 percent in 2000.

The current trend belies notions of the country as a postracial, assimilated society.

Demographers cite a steady flow of immigration that has given Hispanics and Asians more ethnically similar partners to choose from while creating some social distance from whites due to cultural and language differences.

White wariness toward a rapidly growing U.S. minority population also may contribute to racial divisions, experts said.

"Racial boundaries are not going to disappear anytime soon," said Daniel Lichter, a professor of sociology and public policy at Cornell University. He noted the increase in anti-immigrant sentiment after the Sept. 11 attacks as well as tensions over Arizona's new law targeting unlawful immigrants.

"With a white backlash toward immigrant groups, some immigrants are more likely to turn inward to each other for support," Lichter said.

The analysis, by Lichter and others, is based on figures from previous censuses as well as the American Community Survey for 2008, the most recent available. The annual Census Bureau survey of three million households is released each fall.

The figures for "white" refer to those whites who are not of Hispanic ethnicity. For purposes of defining interracial marriages, Hispanic is counted as a race.

Broken down by race, about 40 percent of U.S.-born Asians now marry whites - a figure unchanged since 1980. Their likelihood of marrying foreign-born Asians, however, has multiplied three times for men and five times for women, to roughly 20 percent.

Among U.S.-born Hispanics, marriages with whites has risen from roughly 30 percent to 38 percent over the last three decades. But when it came to marriages with foreign-born Hispanics, the share has doubled - to 12.5 percent for men, and 17.1 percent for women.

In contrast, blacks are now three times as likely to marry whites as in 1980. About 14.4 percent of black men and 6.5 percent of black women are in such mixed marriages, due to higher educational attainment, a more racially integrated military, and a rising black middle class that provides more interaction with other races.