The United Mine Workers union is 100 years old this Labor Day. Richard L. Trumka, its president since 1982, is, at 41, the youngest major labor leader in America.

Last October he took the UMW back into the AFL-CIO, 42 years after John L. Lewis walked out. In January, he gave organized labor what may well have been its biggest victory in years, when the Pittston Co. agreed to settle a bitter 11-month strike and restore threatened health benefits to active and retired coal miners.

The victory made Trumka -- a reform-minded insurgent whose Polish heritage, fiery temperament and bristling moustache invite comparisons to Lech Walesa -- something of a hero to a labor movement notably short of compelling figures. He's in demand as a speaker at conventions of other unions and has been welcomed as a prodigal son by his colleagues on the AFL-CIO executive council, most of them a generation older.

Less than a year after he brought the Mine Workers back into the fold, there is speculation that he will some day bid for the presidency of the labor federation.

But in an interview just before Labor Day, Trumka sounded anything but gloating -- and not only because a Virginia circuit judge had just refused to dismiss $52 million in fines the union had incurred for violating strike restrictions during the Pittston battle.

"This is kind of a bittersweet moment," Trumka said. "At the micro level, a lot of unions, including ours, can be pretty happy. There are some good signs of resurgence -- and of solidarity. ... But at the macro level, we're not organizing on the scale we need to. ... We still have 37 million people without health care. ... We still lead the industrial world in deaths and injuries on the job. ... We haven't been successful with child-care or parental-leave {legislation}. ... And workers in Germany, Japan, Canada, Australia, the Scandinavian countries, Italy, who used to envy our situation, now look at our laws and see they're archaic and hostile to workers."

It is no secret that organized labor has felt beleaguered for the past decade. Ten years ago, unions represented almost one-fourth of the workers; now, barely one-sixth. And three straight Republican presidential victories have taken the formulation and administration of labor laws away from union allies.

Ever since Ronald Reagan fired the striking air controllers in 1981, doubts have grown even about the efficacy of labor's basic weapon. That is why the Pittston strike became so important to all of labor, why AFL-CIO president Lane Kirkland and 18 top officials of other international unions went down to Lebanon, Va., a year ago to be arrested with Trumka in what Trumka called "civil disobedience" and the courts called illegal picketing of the Pittston site.

Long before then, Kirkland had begun telling unionists to stop whimpering about the "hostile" political climate and to use the resources they still commanded to achieve their own goals. But it took Trumka and the Pittston battle to show how it could be done.

The company provided the opening when it decided to use a deadlock in negotiations as an excuse to cancel its contributions to the industry health plan. That plan was supposed to "guarantee" health benefits for retirees, as well as active workers. Pittston's action left 1,500 disabled and retired miners and their families out in the cold.

Trumka and the union exploited that emotional issue to mobilize wide support among churches, community leaders and even other businesses in southwest Virginia. Church meetings, hymn-singing, boycotts and mass demonstrations, reminiscent of the civil-rights movement, fueled the strikers' determination to stay out, despite the fines and arrests for "illegal picketing" and sporadic acts of violence.

At the same time, slick ads were used to mobilize national opinion; even Wall Street investors were asked to pressure Pittston to relent.

Secretary of Labor Elizabeth Dole intervened in the situation, something Republican administrations had refused to do with the equally bitter Eastern Airlines strike and earlier disputes. On New Year's Day she announced a settlement, giving the company some of the work-rule concessions it sought but restoring all the threatened health benefits to the miners.

Trumka is careful not to claim too much for the UMW. "Pittston is not the blueprint for success in every future situation," he told me, "and the victory there does not mean that labor is back and standing tall. But it does show that when working people believe in themselves, what they can do is virtually limitless." Trumka, who worked in the Pennsylvania coal mines before getting his accounting and law degrees at Penn State and Villanova, clearly believes that himself.

"Three years ago," he said, "you'd go to a union meeting and the people you'd see had had all the hope shot out of their eyes. They'd lost faith in their ability to shape their own lives. But now it's starting to come back; you can see it. And that's what's always preceded real social and political change."

It's been a long while since anyone as young as Trumka, with his passion and doggedness and skills, has talked that kind of language in union halls. And that fact alone makes this Labor Day different.