WHERE are we going to put them all? Population is growing all over the world - particularly underdeveloped countries. Who will feed them? Communist China is taking drastic steps to limit its population. It is already the largest in the world. But how about many of the others? You are reminded of it as you leave the Washington National Airport where a clock computer with digital letters grimly announces, WORLD POPULATION IS NOW 4,814,900,891.
The little numbers in the population clock turn menacingly. Tick, tick, tick. In the United States we shall have 282 million by 2000. The population growth rate of the earth is slowing down, but it is still one of the most menacing things on our planet.
President Reagan and the State Department are worried about Latin America. The population explosion has something to do with it. In 1979 Paul Ehrlich and Loy Bilderback in their book, ''The Golden Door'', noted that ''El Salvador, a country about the size of Massachusetts, has 4.5 million people today. . . . The 'Soccer War' between El Salvador and neighboring Honduras in 1969 was formally . . . attributed by the OAS to Salvadoran migrants being pushed into Honduras by El Salvador's skyrocketing population - the first time that population pressure received official mention as a cause of war.''
Was it the first time? One of the most tense spots in the world right now is along the US-Mexican border. Not a formal war but akin to it. According to a recent TV program, by the end of the century Mexico City will be the biggest metropolis on earth. Already, according to the narrator's account, there is barely standing room. The smog in the slums is murky and oppressive. When will they move into the United States? Here is an excerpt from the Federation for American Immigration Reform in its February immigration report:
''Current United Nations projections show . . . a 100 percent rise in population for all the (world's) developing countries, and a 130 percent increase for Latin America between 1980 and 2025. . . . With annual births increasing from 2.7 to 3.2 million by 2020, Mexico's population, even with falling fertility rates, is projected to rise from its present 75 million to 174 million by 2025. . . . What this means for all of Latin America . . . is that the region's population will rise from its present 200 million to 390 million by 2025. . . .''
But can they feed these people? In their scholarly 1973 book William and Elizabeth Paddock answer the question in their title, ''We Don't Know How.'' They recall the 18th-century green revolution in Ireland.
''In the resulting Irish famine of the 1840s, 2 million Irish starved to death, 2 million emigrated, and 4 million were left on the land in poverty.'' What's their comment? ''When such a thing as a Green Revolution occurs, its name will be Disaster if it arrives ahead of the Population Control Revolution.''
Perhaps we are building another disaster on our own southern border. There have been humanitarian calls in the United States to ease Mexican immigration restrictions. US has immigration laws, but their nonobservance is almost as bad as Prohibition. On Feb. 1 the Reagan administration requested 977 additional enforcement officers for the Immigration and Naturalization Service. It is doubtful if Congress will give any such amount. The patrol service is destitute. At any given period only 400 Border Patrol agents guard the entire US-Mexican border. They apprehend over 3,000 illegals a day, and the guess is that for every one apprehended two or three make it across - not only Mexicans but El Salva-doreans. The US has cut down its fertility rate, but because of the influx from abroad (legal and illegal) it has one of the highest growth rates of any industrial country.
America's laws are a paradox. It is unlawful for an undocumented person to work in the US, but it is not unlawful to hire that person. After a decade of bipartisan work the Senate has twice passed a pending comprehensive immigration control bill (Simpson-Mazzoli) and did it by overwhelming majorities: 80 to 19, and 76 to 18.
But the House of Representatives hasn't acted. It might offend somebody in an election year.
The lonely border patrolman grabs the illegal immigrant and brings him into custody. But he fights a war that the nation has forgotten. The world population clock ticks on.