For decades now, the prospect of world overpopulation -- and the impoverishment, resource depletion and ecological damage associated with it -- have dominated our nightmares and permeated our politics. Population control, particularly Third World population, is something on which we all reflexively, vaguely agree. We may argue over whether abortion should be included among the means to achieve it. But the end -- fewer mouths to feed -- is not in dispute.

Maybe it should be. A startling and unjustly overlooked article by Nick Eberstadt in the Public Interest (Fall 1997) explodes the conventional wisdom. Drawing on the United Nations' 1996 report, "World Population Prospects," Eberstadt finds a quite plausible scenario that shows world population stabilizing in 40 years at 7.7 billion (it is just under 6 billion today) and, even more astonishing, declining thereafter.

This scenario posits no war or epidemic or other scourge to do the job. It simply assumes that today's radical decline in fertility worldwide continues. And radical it is. In the developed nations, the rate has fallen from 2.8 children per woman in the early '50s to 1.5 today. In the less-developed nations, it has fallen from 6 to just under 3.

In America, where full-page ads for ZPG (zero population growth) still grace our tonier political magazines, awareness of this historic change has been slow in coming. It has taken a while for Ben Wattenberg's warning about "The Birth Dearth," the name of his 1987 book on the dwindling population of the West, to take hold. On July 10, however, it received the imprimatur of the New York Times in a front-page article highlighting the unprecedented population implosion now taking place in Europe.

Not a single country on the continent has a fertility rate high enough to maintain its current population. Italy, for example, is now the first nation ever with more people over 60 than under 20. In Bologna, there will soon be 25 people over 50 for every child under 5.

Eberstadt estimates that in 1900 the median age in the world was about 20. In the mid-21st century, it will be about 42. And in such countries as Japan, Italy and Germany, the median age will be in the mid-fifties!

Result? Social disaster: children with no blood relatives but their parents; no brothers, sisters, aunts, uncles, cousins. (That's what happens when you have two consecutive generations of single-child families.) Historic disaster: countries losing half their population every two generations. And economic disaster: Not enough working young people to pay the pensions of the old.

And while Europe is committing suicide, what happens to the United States? Here the fertility rate is barely at replacement level. But we are saved -- by immigration.

Immigration is a lifesaver not just for bulking up our numbers. (And raw numbers matter: You can have the highest per capita income in the world, but if you've got no capita, you've got no income.) It illuminates one of the great paradoxes in American life: How is it that our schools are consistently among the worst in the developed world and yet we lead the world in science and technology and R&D in just about every field?

The answer is simple. We import many of our best brains. Walk down any corridor in the laboratories of the National Institutes of Health, for example, and you'll meet the best young minds from every corner of the globe. And many of them stay. Indeed, our computer industry is now begging Congress for an increase in the quota of skilled immigrants to cover our huge shortfall in high-tech workers.

The anti-immigrant demagogues warn that immigration is the road to Balkanization. They are wrong. At the start of this century there were (as a percentage of the population) 50 percent more foreign-born U.S. residents than there are today. And yet the Irish and Italians and Jews and Poles and Chinese and Japanese of that immigrant wave assimilated so remarkably into the American mainstream that today they are the American mainstream.

The problem today is not unassimilable immigrants but an American educational elite that, in the name of ethnic authenticity and multiculturalism, would like them to be unassimilable. Hence the imposition of such devices as bilingual education -- a euphemism for slighting and delaying English instruction -- that not just celebrate but perpetuate ethnic separatism.

California's Proposition 227, effectively abolishing bilingual education, marks a welcome resurgence of American common sense. Immigrants are our future. We owe a duty to them -- and to ourselves as a nation -- to make them American as quickly as possible. We'd better. Immigrants are the magic cure -- the American cure -- for the birth dearth.