They came by the busload today from Maryland's Appalachia -- windburned coal miners determined to abolish a 10-year-old ban on steep-slope mining and impassioned homeowners and conservationists hoping to preserve the state regulation, unique in the nation.

After more than three hours of testimony before a key Senate committee, the only sure thing about legislation to allow steep-slope mining appeared to be its uncertain prospects. Further clouding the bill's future was an announcement by an aide to Gov. Harry Hughes that Hughes opposes the measure.

"I went into this thinking it wasn't going to hurt anything, that you could reclaim" steep coal fields after mining, said Sen. Norman R. Stone Jr. (D-Baltimore County), chairman of the Economic and Environmental Affairs panel that is considering a repeal of a 1975 law prohibiting the mining of slopes steeper than 20 degrees.

But after hearing from opponents of the repeal, Stone added, "It's not as simple as I thought it would be. It's a dilemma."

Stone was one of several committee members who said they were torn between coal producers in Allegany and Garrett counties, who say the ban should be repealed to give their slumping industry a boost, and conservationists who contend the ban serves as an effective curb against further water and air contamination in the long, narrow valleys where coal is mined.

The debate over whether Maryland should lift the ban, the only one of its kind in the country's 26 coal-producing states, has pitted a well-financed coal industry and their lobbyist against a loosely organized band of civic activists in the two counties. Proponents of repeal have said for weeks they believe they have the votes in Stone's committee and a House panel to approve the legislative repeal. Opponents, including some officials of the state Natural Resources Department, believe Hughes would veto the steep-slope bill if it is approved by the General Assembly.

Ellen Fraites, Hughes' adviser on environmental issues, said today the governor opposes legislation to relax the steep-slope ban. But Fraites added that she was uncertain whether Hughes would veto the measure.

"This is a flat-out repeal that would make the environmental risk remarkably greater," said Natural Rescources Secretary Torrey C. Brown. "If we pass this bill we create the potential for problems."

However, a parade of coal-mining experts, including an industry regulator from West Virginia, argued that existing state and federal laws would adequately protect the environment if the ban is lifted. Steep-slope mining in West Virginia has been "consistently successful" largely because of "intensive enforcement," said John Ailes, a senior natural resources official in that state who was brought to Annapolis at the expense of the Maryland Coal Association.

But Jim Ross, 67, a retired pipefitter from Garrett County whose father and grandfather were coal miners, said the ban should be preserved. "Living in the mountains has never been a bed of roses, but mountain people can stay there only if the mountains are cared for," Ross said.