A Congress split by economic and regional differences has proven again that cleaning up air pollution from vehicle tailpipes and industrial smokestacks remains the nation's toughest environmental problem.

Only once since the Clean Air Act was enacted in 1970 has Congress been able to agree on major amendments to strengthen the basic law, and that occurred 11 years ago.Two years ago, environmentalists in the House and Senate renewed the campaign to escalate the battle against urban smog, acid rain caused by coal-burning factories and power plants and toxic fumes from chemicals.

On Tuesday, they tossed in the towel, vowing to try again next year.

"There has not been sufficient willingness to compromise," said Sen. George Mitchell, D-Maine, who spent much of 1988 trying to put together a consensus on a clean air bill. "As a result, we will do nothing."

Mitchell, citing this summer's smog alerts around the country, said the technology exists to control air pollution. "All we lack is the political will to do so."

Among those he cited as resisting compromise were the environmental lobby and the two behemoths that would be most affected by such legislation: electric utilities and the auto industry, domestic and foreign.

Sen. Robert Stafford, R-Vt., a veteran of clean air wars, pointed his finger at Senate Majority Leader Robert Byrd, D-W.Va., who held the Environment Committee's bill off the floor for 11 months while he pushed for concessions for West Virginia's coal.

The bill's death left the nation with no new tools to combat the ozone and carbon monoxide - chiefly from vehicle emissions - that has grown to the point that upwards of 100 urban areas are violating air quality standards designed to protect human health.