WASHINGTON - Americans living in nearly one in five counties nationwide are breathing unhealthy air, according to new ozone rules the Bush administration unveiled on Thursday.

The Los Angeles city skyline is enveloped in smog in this July 15, 2003 file photo. The Environmental Protection agency told officials in 31 states Thursday they must develop new pollution controls because the air in some of their counties, home to more than 150 million people, does not meet federal health standards. The EPA said the Los Angeles basin had the worst smog problem, the only region to be placed in 'severe' pollution category. ( Photo/Jerome T. Nakagawa)

The new standards are generally supported by environmental groups, which have bitterly criticized President Bush's White House for relaxing other pollution rules to benefit various industries.

The Environmental Protection Agency said that 474 of the nation's 2,700 counties in 31 states have unacceptable levels of ground-level ozone, a major ingredient in smog, up from 221 under the previous guidelines. About 159 million Americans live in counties that violate the new standards, the agency said.

Ozone is formed when fumes from automobiles, factories and other fossil fuels react with sunlight. It is linked to human respiratory problems including emphysema and bronchitis.

EPA Administrator Mike Leavitt said the agency notified governors of the 31 states about the violations, which require them to submit smog reduction plans in three years.

"This isn't about the air getting dirtier," Leavitt said. "These new rules are about our new understanding of health threats -- about our standards getting tougher and our national resolve to meet them."

The agency set compliance deadlines based on the severity of the smog. Areas with marginal to moderate pollution have until 2007 to 2009, while highly polluted counties in California get more time. EPA gave smog-ridden Los Angeles and surrounding counties until June 2021 to comply.

The new ozone test stems from 1997 EPA rules delayed by numerous court challenges. The U.S. Supreme Court upheld the rules in early 2001.

The new rules allow less ozone -- 85 parts per billion down from 120 parts per billion -- and require more frequent tests.

HIGHER COSTS

Violating counties would have to spend more on pollution controls such as requiring cleaner-burning gasoline and power plants and more frequent automobile inspections.

The changes mean that about 100 metropolitan areas are in violation of the standards for the first time. They include San Francisco, Denver and many previously compliant suburban and rural areas, the EPA said.

Large swaths of Southern California around Los Angeles and the Northeast corridor between Washington and New York have long been out of compliance.

Some 19 states pass the test, including large swaths of the West around the Rocky Mountains along with Florida, Iowa, Minnesota, Mississippi and Vermont.

Business leaders said the rules could cost states billions of dollars and scare away new industry.

"A non-attainment designation could put a black mark on all of these communities, reducing their business opportunities, investment and competitiveness," said Jeffrey Marks at the National Association of Manufacturers.

Environmental groups applauded the rules, but criticized the flexibility given to some counties.

"It's a positive step that the EPA is going to require stronger anti-smog measures in areas that need them," said Howard Fox, an attorney at Earthjustice. "But they didn't take the next step, which is to set clear firm deadlines for cleaning up those new areas."

© Copyright 2004 Reuters Ltd

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