WASHINGTON — The Environmental Protection Agency proposed stricter daily limits Tuesday for how many microscopic particles of air pollution, or soot, are safe for all Americans to breathe from the nation's smokestacks and tailpipes.

The proposed new health-based air standards represent one of government's most far-reaching decisions. They affect millions of lives, and could force states to make industries spend billions of dollars to clean up coal-burning power plants, diesel-powered equipment, trucks and industrial boilers.

Health and environmental groups had sued the government to force it to tighten its limits. Meeting a court-ordered deadline of midnight Tuesday, EPA ignored the recommendations of an expert clean air scientific advisory committee, which in June called for even tougher limits.

Once the EPA finishes its rule-making next September, states must order cleanups in at least 50 counties, mainly in southern California, the Midwest, the South and the Northwest, EPA studies show.

Stephen Johnson, the EPA administrator, said his decisions were based on "the best science available to date ... particularly for the most vulnerable among us," despite the science advisers' recommendation for a tougher standard. He did not elaborate.

Johnson said he recognizes the science continues to evolve, so his agency would continue to review new scientific findings before it issues a final rule. The EPA also will allow for 90 days of public comment. "This proposal is yet another step to ensure that Americans have cleaner air and healthier lives," he said.

At stake are public health standards addressing fine pollution particles 2.5 micrometers or smaller, which lodge in people's lungs and blood vessels. The EPA said in 1997 that cutting fine particle pollution would save 15,000 people a year from dying prematurely from heart and lung diseases aggravated by soot-filled air.

The 1997 standards currently in use say that industry annually can't release air pollution with fine particles averaging greater than 15 micrograms per cubic meter. On a daily basis, its releases of soot can't exceed 65 micrograms per cubic meter.

The two sets of limits, one for daily exposure to soot and one for annual exposure, are based on scientists' measures of the number of premature deaths, heart attacks, lung cancer, asthma attacks and other illnesses that might result. Then EPA policy-makers decide what's acceptable.

The expert advisory panel had recommended tightening the annual standard to 14 micrograms per cubic meter and the daily limit to 30 micrograms per cubic meter. Health and environmental groups pushed for an annual standard of 12 micrograms per cubic meter -- which was adopted by California and also recommended by some Northeast states.

Instead, the EPA said Tuesday it was proposing to keep the annual limit at 15 micrograms per cubic meter and adopt a new daily limit of 35 micrograms per cubic meter. An EPA staff paper said that would result in 22 percent fewer premature deaths in nine cities.

It also said it was rescinding a broader rule aimed at reducing fine particle pollution 10 micrometers or smaller, because the rules for smaller-sized soot are more effective. The EPA is considering replacing it with a standard that might exempt agribusiness.

Critics said, however, that the differences in the numbers for the current and proposed EPA standards are not as small as they seem. They said the new limits are too soft and show EPA catered to intense lobbying from electric utilities, rather than satisfy the health and environmental groups who had sued the agency in March 2003.

The nine groups, led by the American Lung Association, Environmental Defense, Natural Resources Defense Council and the Sierra Club, wanted EPA to update its eight-year-old standards by proposing the highest levels of soot that could be allowed in the air and still protect public health.

The Clean Air Act requires the EPA to review the adequacy of its health-based national air quality standards every five years to ensure they are up-to-date in reflecting the best available medical science.

"The old standard was so weak that there was room to lower the number without actually making big improvements on the ground," said Dr. John Balbus, an internist and health program director for Environmental Defense. "And what really matters here is reducing people's exposures to fine particles, not just changing numbers."

If the EPA had set the tougher limits a panel of scientists recommended, at least 147 counties -- most of them scattered throughout the East -- would have been affected, according to EPA data. That would help address sooty air in large urban centers like Houston and in some of the larger cities in the interior West.

Dan Riedinger, a spokesman for the Edison Electric Institute, representing utilities, said stricter regulations "may yield limited, if any, tangible benefit to public health" because soot pollution is not as great a threat as it was eight years ago.

In contrast, he said, the costs to industry "can hurt local businesses, drive away new ones, and inflict severe penalties on areas unable to quickly reach compliance."

Source: Associated Press