IN HIS PRESENT bridge-burning mood, David Stockman is speaking much economic truth. He says that the country has more farmers than it can use, and they have invested too much in their land and equipment. There are going to have to be large losses, he further says, and some of those farmers are going to have to find other lines of work. But to listen to Mr. Stockman on the subject of the farmers is to be reminded that good economics is often at war with good politics, and the politicians are not always wrong.

The question for public policy isn't whether people are going to be pushed out of farming. That's been going on since the years before World War I, and with the steady rise in farm productivity it's not going to stop now. For half a century the federal government has provided shock absorbers to slow this process and to make it less painful. But those shock absorbers are expensive. Mr. Stockman is also right in saying that this forced displacement of labor is the sign of a dynamic economy. Economists usually talk as though people welcomed economic growth. People welcome higher pay for what they're used to doing, where they're used to doing it. But economic growth strikes a much harsher bargain. It makes a society richer, but only by requiring people to leave their accustomed ways of life. It imposes immense strain on the people directly caught in it, a kind of cost to which economics pays little attention.

Governments, including the one in which Mr. Stockman is a prominent figure, try to hold a balance. If they try too hard to stave off change with regulations and subsidies, the economy stagnates. If change proceeds too fast, they risk social explosion. That's what happened in Western Europe in the late 1960s. After two decades of the fastest economic growth in European history, a spontaneous rebellion against growth erupted with riots and strikes in France, massive demonstrations in Italy and a surge of terrorism in both Italy and West Germany. But not in Britain, where growth rates had remained low. Since then, the emphasis in Europe has shifted to social stability.

That's why the European Common Market, with a labor force just about the same size as the United States', still has more than twice as many farmers. And that in turn is why the Europeans now have vast unmanageable and unsaleable agricultural surpluses representing a tremendous waste of labor, tolerated for social reasons but imposing a severe penalty on economic progress.

Mr. Stockman advocates doing away with the shock absorbers. Here he speaks as a true economic radical in behalf of pure efficiency. But that's a pretty brutal prescription. The American practice is to do enough to avoid widespread despair throughout the Farm Belt, but not nearly enough to hold all the present farmers on the land. Farm policy is one area of government in which half-measures work best.