CONTROLLING POLLUTION is good for your health, but it's not inexpensive. Last year Americans spent about $77 billion for clean air, clean water and waste disposal. That's a substantial figure, roughly the same as the Defense Department's procurement budget. Or the total of all the doctors' bills that year. Perhaps the doctors' bills are a better comparison, for the driving purpose of the pollution regulations is to prevent illness.

Four-fifths of the cleanup money is spent not by the government but by private businesses and consumers to meet federal and state environmental regulations. That $77 billion includes the catalytic converters in new cars and the extra cost of the unleaded gasoline that they require. It includes municipal sewage plants and the scrubbers that take most of the worst pollutants out of power plants' smoke.

The outlay on pollution control, now approaching 2 percent of GNP, is large enough to affect the way the economy works. What does the country get for its money? The most demonstrable improvements have been in air quality. The concentrations of one particularly toxic pollutant, sulfur dioxide, have fallen sharply since the early 1970s, when Congress began to go after it. Simply to have held air pollution constant over the past 14 years would have been a great achievement, because electric power consumption has risen by a third in that time and the number of motor vehicles by nearly half.

Progress in improving water quality has been uneven, but there have been striking improvements in some areas. The Potomac River is one example of success.

The cost of pollution abatement and control rises steadily. The Commerce Department economists who track these figures estimate that since the early 1970s, total public and private spending on it has gone up an average of 3.5 percent a year after inflation. That's not beyond the country's capacity, but the amounts are large enough to require careful consideration of the way that the program is evolving.

Among many environmental dangers, where can the next billion dollars be spent most effectively? The country is, for example, spending too much on cleaning up toxic waste dumps and not enough on indoor pollution and the threat of radon gas. Environmental policy is now running mostly on past momentum. The country is doing a very respectable job with the pollutants that it identified in the past decade, but there's no clear sense of future direction guiding this gigantic partnership of public and private spending.