When the Census Bureau released its new population projections last month, most of the media focused on the country's changing racial composition. But this was almost certainly not the most important finding. The projections show that the U.S. population will grow by 135 million in just 42 years -- a 44 percent increase. Such growth would have profound implications for our environment and quality of life. Most of the increase would be a direct result of one federal policy -- immigration. If we reduced the level of immigration, the projections would be much lower. The question we have to ask ourselves is: Do we want to be a much more densely settled country?

Native-born Americans have only about two children on average, which makes for a roughly stable population over time. But with an estimated 1.5 million legal and illegal immigrants settling in the country each year, and about 900,000 births to these immigrants each year, immigration directly and indirectly accounts for at least three-fourths of U.S. population growth.

An increase of 135 million people by 2050 is equivalent to the entire populations of Mexico and Canada moving here. Assuming the same ratio of population to infrastructure that exists today, the United States would need to build and pay for 36,000 schools. We would need to develop enough land to accommodate 52 million new housing units, along with places for the people who lived in them to shop and work. We would also have to construct enough roads to handle 106 million more vehicles.

Of course, our country can "fit" more people. But such a dramatic increase would affect many issues about which Americans are concerned, including the environment, traffic, congestion, sprawl and the loss of open spaces. Technology and planning could help manage this situation, but there is no way they could offset all of the impact of 135 million more people. This massive increase also would have implications for the size and scope of government; more densely settled societies almost always are more heavily regulated societies.

Another important finding in the census projections is that, even with record levels of immigration for the next four decades, the U.S. population will still grow significantly older. Immigration makes our society only slightly younger than it would otherwise be. (Consider that, on average, the overall fertility rate in the United States is about 2.1 children per woman. If immigrants are excluded from the data, it's still about 2.0 children per woman. This compares with 1.4 children in Western Europe. Immigration makes for a much more densely settled country; it does not make for a much younger country.) As the Census Bureau stated in its 2000 projections, immigration is a "highly inefficient" means for addressing the problem of an aging society in the long run. The new projections show the same thing.

Some people think that immigration creates large economic benefits. But the economic research is pretty clear: While immigration does significantly increase economic activity in the receiving society, almost all of that increased activity go to the immigrants themselves in the form of wages and benefits. The gain to natives is tiny. When the National Research Council, which is part of the National Academy of Sciences, examined this question, it concluded that the benefits for native-born Americans were equal to only about one- or two-tenths of 1 percent of their income. The two economists who did the work for the council described the effect as "minuscule."

Moreover, this tiny economic benefit was entirely erased by the fiscal drain immigrant households imposed on taxpayers. Perhaps worst of all, the researchers found that to generate this small gain, immigration reduced the wages of the least educated and poorest American workers.

There is no question that immigrants benefit by coming here. But it is difficult to argue that immigration is a well-targeted way to lift up the world's poor. Many immigrants to the United States were not poor in their home countries. More important, although immigration causes an enormous increase in the overall U.S. population, it still represents an infinitesimal fraction of the world's low-income population. We can do more to help poor people in developing countries through trade policies and development assistance.

The United States may well decide to continue to allow the settlement of 1.5 million immigrants (legal and illegal) each year. But legal immigration is a federal program like any other and could be reduced below the 1 million currently allowed to enter annually. Greater resources could also be devoted to reducing illegal immigration. It's important to understand that the new projections show us one possible future. We must decide as a country if this is the future we want.