When Gary Hart descends deep into the darkness of the coal-rich ground each day, he fears the future. As a miner, he could lose his job. As mayor, he could lose his town.

The double threat comes from hundreds of miles away, where Congress is rewriting the nation's clean air laws, setting new pollution standards that could crush this tiny town that lives and thrives on coal.To combat acid rain, the local mine's neighbor and only customer - one of the nation's dirtiest coal-fired power plants - likely will have to reduce the sulfur dioxide spewing from its stacks. How it does that has put Kincaid on edge: hoping for a reprieve, but leery of a death sentence.

"If they shut down completely, I'm not going to have a community to lead," Mr. Hart said. "It'll sit there and die. People will have to move to get jobs. It's just a sad thing. People want to work, they want their jobs, but how do they keep them?"

Across the Midwest and northern Appalachia, high-sulfur coal country, Kincaid and other mining towns are in a quandary, wondering whether new clean air laws will pit health against wealth, reducing prosperity with pollution.

"There is a need for clean air," Mr. Hart said. "But completely wiping out an industry is not the solution to the problem. It just creates a bigger problem."

In Ohio, one congressman recently said acid rain controls could cost the state up to $2 billion a year and raise some commercial electric rates as much as 40 percent. In Kentucky, officials say half the coal mining jobs in the western part of the state could be lost.

And in Illinois, which already lost 30 percent of its coal mining jobs in the 1980s, a worst-case scenario estimates up to 4,500 more could vanish.

The government says up to 5,000 high-sulfur coal jobs likely will be lost nationally by 1995. But the United Mine Workers predicts that will grow to about 20,000 by the end of the decade, inflicting more pain on an industry that has shrunk by 44 percent in the last decade and crushed Main Streets dependent on miners' dollars.

Commonwealth Edison Inc., Chicago, the utility that owns the plant, won't decide how it will reduce sulfur fumes in Kincaid until the clean air measure becomes law.

The Senate passed a bill April 3, the House still is working on the legislation.

Commonwealth Edison can install pollution control equipment called

scrubbers, which would cost about $350 million and cut emissions by about 90 percent, or take two other devastating steps.

One would be to switch to cleaner, low-sulfur coal from the West, the other, to shut down, which would almost certainly trigger the mine closing.

"We're doing everything possible to try avoid closing the plant," said John Maxson, Edison's governmental affairs director.

The stakes are enormous. The plant and Peabody Coal Co.'s mine No. 10, across-the-road neighbors, have nearly 900 workers and an annual payroll of about $25 million, Mr. Maxson said.

Meanwhile, in this town of 1,500 where mining is a tradition, with sons and fathers working side-by-side, the uncertainty has folks fretting.

"You're hanging by a thread," said miner Butch Spinner. "Are you going to fall on the good side of the lake or on the side with the alligators?"

"We're pawns in a big political game," said Ron Phares, 33, a husky 12- year mine veteran. "You feel powerless, pushed aside, neglected.