FORTY years ago, Juarez was a sleepy town of 49,000 in the shadow of El Paso, Texas, just across the Rio Grande. Today, this city has mushroomed into a sprawling metropolis of 1.3 million - nearly three times the size of its Texas neighbor. The story of Juarez is repeated again and again along the United States border. Attracted here by new factories that build everything from automobile bumpers to electric blankets, thousands of young Mexicans are streaming to cities like Juarez, Mexicali, Nuevo Laredo, and Matamoros.
Since World War II, Matamoros has rocketed from just 15,000 people to an estimated 500,000. Nuevo Laredo has soared from 29,000 to 600,000. Mexicali jumped from 19,000 to 1 million. Tijuana grew from 16,000 to 1.2 million.
The population explosion puts mounting pressure on the US. For the first time, millions of Mexicans are living on America's doorstep. Many of them, gazing across the river, are clambering for the good life that lies so near.
Mexico, however, is just part of the story of the surging force of population growth in the third world that could reshape the US.
Around the globe, from African villages to Asian cities, reports of America's wealth are spread by television, books, newspapers, radio, and motion pictures. People in third-world countries drink up American images of suburban homes, modern cars, and good jobs - and they want to share it.
Border patrolmen in Texas report aliens are streaming into America from at least six dozen nations. Many come illegally, taking weeks or even months to reach the US border.
Some scholars say this is good news for the US. It means that old-fashioned American values - democracy, free enterprise, religious tolerance - exude a powerful appeal to people worldwide. At a time when world communism is wilting like a daisy in December, freedom is flowering.
But there is also a challenge for the US. As America's popularity spreads, its citizens must make major decisions about the country's future:
How many new immigrants should the US accept?
What nations should those immigrants come from?
Should immigrants be selected by their skills?
Should family reunification be a major goal?
How many people should the US ultimately have - 300 million? 400 million? 1 billion?
Should current laws, which favor immigrants from South America and Asia, be altered?
What should be done about illegal immigration?
These issues have aroused little interest in Congress. But some specialists, such as Ben Wattenberg and Karl Zinsmeister of the American Enterprise Institute, and immigration analyst Arthur Corwin, are looking for answers.
In December, Mr. Wattenberg and Mr. Zinsmeister released a study that concluded that recent immigration has made the US ``the first universal nation.''
``We are the first nation in history where people come from everywhere.... It is an incredible story. The human poetry of this is astonishing,'' Wattenberg says.
Prior to 1965, most Americans traced their roots to either Europe or Africa. But a change that year in US law opened the door for people from other continents. This led to millions of new immigrants: Hispanics (not just from Mexico, but from Nicaragua, El Salvador, Panama, Colombia, Peru, Venezuela, and the Caribbean); Muslims (the US now has as many Muslims as Jews); Asians (Indians, Chinese, Vietnamese, South Koreans, Filipinos).
About 605,000 emigrate to the US legally each year. The number entering illegally is unknown - but estimates range from 200,000 to more than 1 million.
In some cities where these newcomers have clustered, Americans find the rush of immigrants alarming. The babble of many languages - Russian, Pashto, Hindi, Spanish, Chinese, Vietnamese - echoes on streetcorners and in shopping malls.
America's `secret weapon'
But Wattenberg insists that rapid immigration is America's ``secret weapon'' in the world's economy. To keep America growing, the country needs new, energetic workers. That may require even higher immigration.
The Wattenberg-Zinsmeister analysis notes that America may be ``entering an era of long-term labor shortage'' which only immigration can counteract. They note that from mid-1985 to mid-1989, the US created about 11 million new jobs, while the working-age population grew 5 million.
``If that squeezing trend continues, it will become ... difficult for employers to fill new positions.... In many areas, grave labor shortages already exist.''
Europe and Japan, which are America's primary competitors, face similar labor shortages that could slow their economies, Wattenberg says. But America, willing to accept peoples of all cultures, races, and religions, can continue moving ahead.
In fact, America is so popular with potential immigrants that this country can pick and choose - selecting those people as new citizens who possess needed skills.
``There is nothing to prevent American immigration policy from being tied closely to the nation's social and industrial needs,'' Wattenberg contends.
Without higher levels of immigration, it is estimated that the US population will peak in 2030, then decline. Yet Wattenberg says the US needs a rising population in the 21st century to maintain its power as a world leader.
Social, political changes
Some specialists on immigration, however, are not so sanguine about higher immigration, or the possibility that the US population could rise above 300 million, as Wattenberg favors.
Dr. Corwin, who is writing a book on immigration, worries that the US already faces serious social and political problems because of both legal and illegal immigration.
Corwin, based in New Mexico, says there is evidence of a ``Mexicanization'' of the Southwestern states. Other regions could face similar challenges.
Corwin suggests that in a nation that had a white, Protestant, European base for so many years, rapid immigration could bring changes - cultural, linguistic, political - which could wrench the nation's foundations in unforeseen ways.
He admits the melting pot is still amalgamating a wide range of peoples, from Koreans in California to Russians in New York City.
But not every development is so favorable. Growing demands for bilingual education, for multi-lingual ballots, and for official recognition of the Spanish language are all warning signs that the melting pot could boil over, he says.
Corwin isn't calling for a halt to immigration. But he is saying: Go slowly. Think about the dangers. Keep immigration under control.
Thus, the debate about America's future has begun. All sides agree on one thing: Immigration could be the most important outside force shaping the future of the US through the next century.