By the midpoint of this century, America will look much like California does today as it morphs into a far more racially and ethnically diverse nation that will owe most of its population growth to immigrants and their offspring, according to a recent report.

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	One study says immigration will account for more than 80% of the growth between 2005 and 2050. CNS Graphics.

By 2050, nearly one in five of the projected 438 million Americans is expected to be foreign-born, a proportion higher than at any other time in U.S. history. Whites will lose their majority status.

The Washington, D.C.-based Pew Research Center, which compiled the demographic forecast, was careful to stay clear of making pronouncements about the data's significance, acknowledging only that immigration will dramatically alter the nation's demographic profile.

The center's conclusions, though, will be certain to fuel debate over the country's immigration policy, demographers said.

''In California, we're the precursor of what's projected to be happening for the rest of the country for the next half century,'' said professor John Weeks, director of San Diego State University's International Population Center.

''You put this out there, and it will influence policymakers regardless of which side of the immigration debate you're on. This is the wake-up call that the anti-immigration policymakers were looking for. They'll feel like if we don't do something now to stem the tide of immigration, then this country will be like a foreign country in the future.''

Weeks, however, said he suspects that the Pew researchers have overestimated the sheer volume of future immigration, given the marked decline in Mexico's fertility rates in recent years.

Key among the Pew Center's findings is that 82% of the 142 million additional people who will be in the United States by 2050 will be immigrants and their American-born descendants. Of that number, 67 million will be the immigrants themselves, 47 million will be their children, and 3 million their grandchildren, according to the forecast. The U.S. population will become more diverse as the number of Latinos triples in size, accounting for 29% of the population in 2050, compared with 14% in 2005.

In 2050, 19% of the nation's population will be foreign-born, the Pew Center projects.

Asians will experience rapid growth in population as well, nearly tripling in size by 2050, when they will represent 9% of the country's population, compared with 5% in 2005.

Also highlighted in the report is the nation's older population, which is projected to more than double by 2050. The number of people age 65 and older is expected to grow from 12% of the population to 19%.

Especially telling are the Pew Center's conclusions about the role of immigration on the labor force. Future immigrants and their U.S.-born descendants will account for all growth in the country's working-age population of adults between 18 and 64.

Put another way, if there were no new immigration, there would be a decline of 7 million people in the working population, the Pew Center found.

''It's very important for our labor force to have immigrants come to the United States,'' said demographer William Frey of the Washington, D.C.-based Brookings Institution. ''But what it doesn't show is whether immigrants will be able to fit the kinds of jobs needed to keep America ahead of the curve in the global economy.''

While the report's authors did not differentiate between legal and illegal immigration, the growth rate takes into account the estimated 11.5 million to 12 million illegal immigrants living in the United States, as estimated by the Pew Hispanic Center in 2006.

The projected growth rate is a testament to the ineffectiveness of current border policies, said Wayne Cornelius, director of the Center for Comparative Immigration Studies at University of California San Diego.

''It is an additional corroboration of the failure of the border enforcement build-up to reduce the rate of growth in the stock of undocumented immigrants,'' Cornelius said. ''If that stock weren't still growing by nearly half a million a year, these projections would be a lot lower.''

The Washington, D.C.-based Center for Immigration Studies, which favors restricting immigration, released its own report last year using U.S. census data, predicting that if current levels of immigration continued, immigrants and their descendants would account for 63% of the increased population between 2007 and 2060.

While the executive director of the Center for Immigration Studies acknowledged immigration's role in boosting the nation's work force as the population ages, he said it is not sufficient to justify a much larger population overall, considering the potential effect on the nation's resources.

''The question is, do we want to have a government policy that will increase the population by 100 million?'' Mark Krikorian said. ''We need to ask the question in that way. That means 80 million more cars on the road. That means 40 million more homes that will have to be built on what is now open land. We have plenty of space for more of this, but from a quality-of-life point of view, do we want that?''

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