United Mine Workers President Richard Trumka wound up a weeklong demonstration against Pittston Coal Group Inc. at Charleston, W. Va., by promising to broaden the two-month-old miners' strike. "There's no doubt in my mind that it's going to expand," Trumka told a rally of about 12,000 strikers and their sympathizers. He would not say whether he would take the strike to other parts of the country, such as Kentucky, where about 200 Pittston miners remain on the job. On the final leg of a six-day march, Trumka led supporters to the state Capitol, where Gov. Gaston Caperton urged a compromise in the dispute over wages, benefits and work rules.