FIGURES JUST released by the Census Bureau confirm what professional demographers have known for some time: world population growth is slowing down. There were, the Census Bureau believes, some 4.7 billion people in the world this June --82 million more than last year. But that represents a growth rate of only 1.8 percent. At the beginning of the 1970s, the growth rate was 2.2 percent. It doesn't sound like much of a difference, but it made a lot of difference in the quality of life in dozens of less developed countries.

The typical pattern in these countries, and in the world as a whole, had been for death rates to drop because of improved medical care, while birthrates stayed high. Then, as time went on, birthrates too went down. In some places--notably sub-Saharan Africa--population is still increasing at record rates. But in others--notably China, India, and Latin America--the rate of population growth is slowing. Sometimes, in India and China, for example, some of that slowdown is the result of practices Americans would find repugnant, such as compulsory sterilization or even infanticide.

It should be understood that a rising population is not necessarily a bad thing. The East Asian fringe-- the non-communist countries from South Korea down through Taiwan to Thailand, Malaysia and Indonesia--has had one of the highest population growth rates in recent years, and one of the highest economic growth rates as well. Economic growth in those countries is running well ahead of the number of mouths to feed, and standards of living are rising. It may be that here, as in Western Europe and North America in the 19th century, the same attitudes--optimism and faith in the future--are contributing to population and economic growth. Latin America's very rapid population growth was accompanied, until the recent worldwide recession, by substantial economic growth; everyone in the United States has an economic stake in having that growth continue.

Some 49 percent of the people on Earth live in just four countries: China, India, the Soviet Union and the United States. But only one has an above-average population growth rate. The big gainers in upcoming decades are likely to be the next countries on the list: Indonesia, Brazil, Japan, Bangladesh, Pakistan, Nigeria and Mexico. The "Western" share of world population is declining, but if these growing nations grow economically, then the long-run prospect is for a more prosperous as well as populous world.