AS THE CENSUS Bureau now points out, the American population is a round quarter of a billion. It has doubled since 1932 and continues to grow rapidly by the standards of the rich industrial countries. There's an endless quarrel among the states and cities, not to mention their representatives in Congress, as to whether the bureau's numbers are precisely the right ones. But that's a zero-sum game, for the congressional seats and federal dollars that census-based formulas give to one jurisdiction are taken away from others. While that dispute is more immediate, it's less interesting than the broad pattern of this growth and its implications for American national life.

The population is currently rising nearly one percent a year, and more than three-fourths of it is natural increase -- births minus deaths. The rest is immigration. If present trends continue, the rate of natural increase will fall from decade to decade on a track that would bring the population to 300 million some time around 2025 and then level off around 310 million in the second half of the next century.

Predicting birth rates is not easy, but in recent decades they have generally fallen as women became more highly educated and as they took jobs. Since there's no reason to think that levels of education and employment won't continue to rise among women, it's plausible to expect lower birth rates -- at least in the absence of great disruptive events. World War II and post-war prosperity sent birth rates soaring, a phenomenon that no demographer had anticipated. But barring that kind of upheaval, drastic changes in the rates seem unlikely.

Immigration is harder to predict, since it depends entirely on public policy. In this century the country has gone through several sharp swings of sentiment, and over the next century perhaps there will be more.

The character of a country's life is greatly affected by the scale of its population. The first American census, in 1790, reported 3.9 million people. It is not the least of the Constitution's genius that a scheme of representation conceived for a small, mostly rural population has adapted itself successfully to a huge, mostly urban one. But that growth has certainly changed the nature of representation, rendering it less personal and direct.

Population growth generates issues and concerns of its own. The environmental movement, and the passion for preserving the wilderness, draw some of their strength from a sense of crowding that was much less widespread in this country a generation ago. But it's still far from a crowded country. Even at 310 million the United States would remain, among the world's highly developed democracies, one of the least densely settled.