A bitter, year-long campaign ends today when members of the United Mine Workers of America decide whether to keep their tobacco-chewing president, Sam Church Jr., or replace him with a young Pennsylvania lawyer, Rich Trumka.

It is a choice of sharply contrasting personalities and outlooks on the direction of the storied, 200,000-member union.

Church, 46, a beefy former mine electrician who worked his way up through the ranks, has presided over a period of relative peace in the coal fields and last year negotiated a lucrative contract that provides working miners with a 33 percent wage-and-benefit increase over three years. Some coal miners can now receive more than $100 a day.

At the same time, however, the coal industry -- like autos and steel -- has been dragged into recession, and more than 30,000 miners have been laid off.

Also, Church has generated controversy with his stated intention to depart, in the next negotiations, from the union's credo of "no contract, no work." He proposes instead to delay any strike until the large coal stockpiles built up by management are depleted.

Church took over the union in 1979, after ill health forced Arnold Miller to retire. He led the union through one 72-day strike.

Trumka, 33, has accused Church of giving up too many union and job-security provisions in return for the financial improvements in the last contract. He has also criticized Church as a weak organizer, claiming the once-dominant union has organized only 18 mines in the last two years.

With new, non-union mines opening in the West, unionized miners now dig only about 44 percent of the nation's coal, down from 70 percent in 1970.

"The main plank in our platform is, no more backward steps, no more take-away contracts," Trumka says.

Church has countered that Trumka is a militant with leftist associations who encourages wildcat strikes. Church argues that the export market for coal "has increased because we have a stable market, and we've got to keep it that way."

Trumka, a member of the union's International Executive Board, comes from a coal-mining family, but left the mines after three years to become a union lawyer. His law degree is from Villanova University.

A bachelor who wears business suits, Trumka doesn't smoke or drink. He lives with his parents.

The bearded Church, by contrast, has a reputation as a rough-cut, soft-spoken man who, in the tradition of the dangerous and dirty coal-field life, has used his fists on occasion to settle an argument.

Church aides believe the race will be decided in West Virginia, where more than one-fourth of the union's membership lives.

Trumka is believed to be more popular among younger miners, while Church, who won a pension for miners' widows, reportedly is favored among the 60,000 pensioners allowed to vote.

The campaign has heated up in its final days. Church, for example, has mentioned that the Socialist Workers Party favors Trumka, adding, "They judge you by the company you keep."

Trumka has denounced as a smear campaign charges by Church supporters in West Virginia that his side has ties to communist or socialist groups.