A century from now, the United States will have twice as many people, the young will no longer outnumber the old and members of today's minority groups will be in the majority, according to Census Bureau forecasts to be released today.

Immigration will still drive population growth, but fewer new Americans will come from Central and South America, and more will come from Asia, the Middle East and Africa, the forecast says. And even amid this roiling racial and ethnic change, different groups will become more alike in important ways, according to a variety of demographers.

The Census Bureau forecasts, issued at the dawn of a new century, are the first to propose a glimpse of the future 100 years away. By mid-century, the United States will have about 404 million people, and 571 million by 2100, compared with today's 275 million. Members of today's minority groups will account for 60 percent of the population. The numbers of people under 18 and people over 65 will be about the same, whereas now there are twice as many children.

Census Bureau demographers say they used trends already in motion, such as immigration, the aging of society, the tendency toward smaller families and advances in longevity. But forecasting is a flawed art, especially so far into the future. Even a small change in government policy or individual behavior, not to mention a disaster of some kind, could swing the numbers dramatically.

The new projections, some say, raise concerns that growth will strain the environment, public facilities such as highways and schools and the public's patience. Census Bureau demographers, though, offered reassurance that a doubling of the population is not necessarily cause for alarm.

"Our projections for 2100 will give us a population density one-quarter of the United Kingdom," said Frederick W. Hollmann, a Census Bureau demographer. "We'll still be a sparsely populated country among the industrialized countries of the world."

Census Bureau forecasters did not estimate which regions would see the most growth, but some said the increase is sure to worsen sprawl, traffic congestion and other urban ills.

"It's just amazing," said Steven Camarota, research director for the Center for Immigration Studies, which advocates controls on immigration. "Unless one postulates massive high-rises, you have got to have an enormous amount of rural and undeveloped land converted to suburban land."

Jeffrey Passell, a demographer at the Urban Institute, said much depends on where the new jobs are, which is especially important in attracting immigrants.

"Depending on the micro- and macroeconomic conditions, we might see some new centers," he said. "That having been said, the bulk of the immigrants go to where the immigrants already are."

Just as it has in past projections, the Census Bureau says the nation's population will age quickly, especially as the baby boomers reach their sixties over the next three decades. By 2100, there will be more than 5 million Americans who are at least 100 years old; today, there are about 65,000. The number of children will grow, the projections say, but not as quickly.

Census Bureau experts continue to forecast that growth of the nation's minority groups will outstrip that of its non-Hispanic white population, due to immigration, larger families among minorities and improved life expectancy. Latinos are predicted to be the nation's largest minority group by 2005. No single minority group will outnumber non-Hispanic whites over the next century, however.

The nation's mix of immigrants will change radically in coming decades, the Census Bureau predicts. The huge influx from Central America is predicted to slow within the next two decades, when current U.S. residents have brought over all the relatives the law permits.

After 2020, the Census Bureau predicts higher immigration levels, in part to supply enough workers to balance the aging baby boom. As in recent years, the new immigrants will not come from Europe, but from other parts of the world, Census Bureau experts predict.

Immigrants are now 10 percent of the U.S. population but are predicted to grow to 13 percent in 2050.

Overall, Census Bureau and other demographers predict that the nation's racial and ethnic groups will grow more alike in time. For one thing, intermarriage will blur identification lines, possibly making today's racial categories irrelevant. But demographers also say it's part of the assimilation process for immigrants to want smaller families and move up the economic ladder.

"There are a lot of things going on," Hollmann said, "to occupy the attention of planners."

Populating the Century

The Census Bureau has released new predictions that say the nation's population could more than double by the end of this century, and that there could be major changes in the country's racial and ethnic makeup.

Population predictions

In millions

2000 275

2050 404

2100 571

(In millions) 2000 2050 2100

Non-Hispanic whites 197 213 230

Black/African American 35 59 86

Asian 11 38 75

American Indian 2 4 6

Hispanic (all races) 32 98 190

Children 70 96 130

People 65 and over 35 82 131

NOTE: The racial and ethnic groups above do not add up to the total population because Hispanics can be of any race.

SOURCE: Census Bureau