THE UNITED Mine Workers have voted out their union president, Sam Church, and voted in Richard Trumka, a 33-year-old lawyer and onetime miner, by more than a 2-1 margin. That's a landslide in any election, especially in union leadership contests, which incumbents almost always win. What does it mean?

To answer, you need to understand two things. First, this is a union with a history of turbulence in the last decade. The membership rejected a contract negotiated in 1981 by Mr. Church, and earlier the union was plagued by wildcat strikes. Second, this is a union which has, for all its dissatisfaction, achieved high wage increases in the 1970s. Together with auto workers and steel workers, union coal miners have won the nation's biggest wage increases. Their success seems to have made them hungry for more. Mr. Trumka, like most insurgent candidates in union elections, did not run on a platform of "less." He argued that Mr. Church had not gotten big enough settlements, and that he would do better.

It is not clear that Mr. Trumka can deliver on this promise. Auto and steel workers' unions found that they had to pay a steep price for the high wages employers agreed to. They lost sales to imports because labor costs were uncompetitively high, and hundreds of thousands of workers lost their jobs. Coal miners today do not have to worry about this type of competition in the short run: coal is cheaper now than oil or other fuel sources, and the market for labor-intensive eastern coal is to some extent protected by, of all things, the Clean Air Act. But union coal does have one effective competitor: non- union coal. In 1970, union miners dug 70 percent of the nation's coal; now the figure is 44 percent, and 35,000 miners have been laid off. Mr. Trumka complains of these trends, but will his pledge of "no more backward steps, no more take-away contracts" make union coal more competitive?

The election results suggest that UMW members refuse to accept the fact that the coal industry does not exist in a vacuum and that miners' wages ultimately depend on the competitiveness of the product they produce. It is a fact others like to ignore: the Chrysler workers who are striking in Canada, for example. Some of this attitude is rooted in an old-fashioned suspicion that the boss is hiding a big pot of money, and if you're tough enough he'll have to fork it over. There may be something to that -- but not much. The financial situation of publicly held companies in this country is anything but a secret; union members can read the business pages as easily as anyone else. Sometimes workers can share what are, in effect, monopoly profits and win big wage increases as auto, steel and mine workers did in the 1970s. But eventually such monopolies come to an end. Mr. Trumka is going to have to explain that to his new constituents sooner or later, or he will likely receive the same treatment as Mr. Church.