Asians and Hispanics will see the most dramatic increases between now and midcentury, when the U.S. population will have grown by almost 50 percent to reach 420 million, according to bureau projections being released Thursday.

America will get older, too. Nearly 21 percent of its residents will be age 65 or older, compared with 12 percent now.

The data highlight trends long predicted. But racial and ethnic changes are taking shape faster than expected, due in large part to higher-than-forecast immigration rates for Asians and Hispanics, said Greg Spencer, a bureau demographer.

Whites now represent 69 percent of the population, but their growth is slowing because of low rates of birth and immigration. Their total will grow 7 percent to 210 million, or 50.1 percent of the population, in 2050.

Those figures do not include Hispanics. The Census Bureau counts "Hispanic" or "Latino" as an ethnicity rather than a race, so they can be of any race, including white.

Between 2040 and 2050, the Census Bureau expects the non-Hispanic white population actually will decline slightly because of a large number of expected deaths of baby boomers, who by 2040 will be at least 76.

Meantime, the Hispanic and Asian populations are expected to continue their explosive growth.

The Asian population is expected to more than triple to 33 million by 2050. Hispanics will increase their ranks by 188 percent to 102.6 million, or roughly one-quarter of the population.

"Historically, we've been a black-and-white country. That's not true any longer, and even less true in the future," said Roderick Harrison, a demographer with the Joint Center for Political and Economic Studies in Washington, which studies issues of concern to minorities.

"A good deal of social history in the next several decades will be reflected in how we sort that out, whether we achieve greater degrees of equality in these populations," he said.

The projections — the first released by the bureau since the 2000 head count — also show a burgeoning older population as healthier lifestyles and better medical treatment increase longevity. By 2050, 5 percent of the country will be 85 or older, compared with 1.5 percent now.

"This poses very interesting challenges. Institutions are going to be transformed — and Social Security is the obvious one," said demographer Martha Farnsworth Riche, a former Census Bureau director. She pointed to education and health care as other affected areas.

Factors such as how multiracial Americans are counted could drastically alter these predictions, Riche and Harrison said.

Prior census data show that most Hispanics choose white as their race. Riche said that could be a sign that future generations of U.S.-born Latinos would select white and rather than Hispanic as their background as they move further from the generation that first immigrated to the United States.

"When you look at 2050 and possibly see a large Hispanic population that doesn't speak Spanish anymore, being Hispanic might be something very different from today," Harrison said.

The bureau expects the black population will rise 71 percent to over 61 million, or about 15 percent of the population, compared with nearly 13 percent now. Blacks would remain the second-largest minority.

Asians would comprise 8 percent of the population in 2050, compared with 4 percent now.