President Bush, fulfilling a campaign pledge to clear America's polluted skies, signed a historic clean air bill that will require deep and costly cuts in urban smog, acid rain, toxic hazards and ozone depletion.

As he placed his signature on the legislation, a difficult compromise between economic and environmental interests that will touch virtually every major industry, Bush called it "truly a red letter day for all Americans" concerned about cleaner air."This bill means . . . a cleaner America," he declared Thursday before an array of administration, congressional and industry and environmental officials who helped make the signing possible.

"Virtually every person in every city and every town will enjoy its benefits," Bush said. "It is simply the most significant air pollution legislation in our nation's history, and it restores America's place as the global leader in environmental protection."

The bill largely follows the outlines of the clean-air plan Bush sent to Capitol Hill last June - an initiative cited as the key factor in breaking the 13-year stalemate in Congress over strengthening and updating the 1977 Clean Air Act.

Approved 89-10 by the Senate and 401-25 by the House last month, the new law will tighten pollution controls over the next two decades at a vast array of industrial and commercial facilities, ranging from steel mills to power plants to the corner dry cleaner and gasoline station.

It also forces carmakers to build less-polluting automobiles and the oil industry to make cleaner-burning "reformulated" gasoline, a double whammy expected to raise the cost of driving.

In signing the bill despite warnings that it will cost thousands of jobs and accelerate the nation's economic downturn, Bush pointed to the thickening air pollution that is exacting an even more fearsome toll in disease and premature death for an estimated 50,000 Americans a year.

"We all had tough choices to make," he said. "Some said we went too far and others said we didn't go far enough. But despite our differences, we all agreed on the goal: clean air for all Americans. And we agreed on the means: a new Clean Air Act."

Environmental organizations and businesses continued to debate the merits of the bill as Bush signed it into law.

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Objectives of Clean Air Act

The legislation seeks by the turn of the century to:

- Halve sulfur dioxide emissions from 111 coal-burning power plants in the Midwest, Southeast and Appalachia that have been identified as the major cause of acid rain damaging lakes, streams, forests in the Northeast and Canada. It is the first U.S. effort to combat acid rain.

- Achieve a 75 percent cut in 189 toxic or cancer-causing chemicals now routinely emitted by 250 different industrial sectors, including garbage, hospital and toxic waste incinerators. The bill gives new teeth to the previously ineffectual federal program to cut the 2.4 billion pounds of deadly air pollutants discharged by industry each year.

- Eliminate chlorofluorocarbons and three other widely used industrial substances that erode Earth's protective ozone layer. The phaseout schedule is slightly more aggressive than that required under an international treaty to protect Earth's ozone layer.

- Clean up most of the 96 cities where smog now exceeds federal health limits. The dirtiest nine of the 96 would have slightly longer to come into compliance, with Los Angeles, the nation's smoggiest city, having until 2010. The bill tightens emission limits on big factories and extends controls to smaller facilities such as gasoline stations and print shops in the most polluted areas.