WASHINGTON -- The Environmental Protection Agency is continuing its crackdown on coal pollution with a new plan to cut sulfur dioxide -- a move that would clean up the air for millions of Americans and bring some relief to people who suffer from asthma and other respiratory diseases.

The new rule, proposed this month, would be the first time since 1971 that the EPA has tightened controls on sulfur dioxide to protect the public health.

"This would be an important step to ensure the health of the American public," said Dr. Alan H. Lockwood, a University of Buffalo neurology and nuclear medicine professor. "Tens of thousands of Americans die each year from inhaling pollutants from coal burning."

By targeting coal pollutants, the EPA is cleaning up the fuel that generates half the electricity generated in the United States. Earlier, after a series of court orders, the EPA said it would require power plants to eliminate mercury pollutants. Now, the public and industry officials will be able to comment on the sulfur dioxide proposal. A public hearing is set for Atlanta in January.

In making its case for tougher regulations, the EPA's science advisers said research over the past 35 years shows that current regulations didn't protect public health enough, and that the estimated health benefits would greatly outweigh new costs to industry.

Sulfur dioxide is emitted by coal-fired power plants and industries. Fossil-fuel combustion at power plants produces 66 percent of the sulfur dioxide in the air, the EPA reported. Most of the rest is from burning fossil fuels for industry, but smaller amounts of the pollutant also are released from other industrial processes, such as extracting metal from ore, and use of high-sulfur fuels by locomotives, ships and non-road equipment.

Sulfur dioxide in the atmosphere converts into fine particle pollution that penetrates the lungs and can cause or worsen lung diseases. Exposure to the pollutant even for a short time can make it hard for people with asthma to breathe when they are active outdoors. The scientific reports also show that children and adults over 65 and people with heart or lung disease are at the greatest risk.

The old rules set limits for sulfur dioxide as averages measured over 24-hour and one-year periods. The new, more protective rule would require one-hour measurements. As a result, short-term spikes of the pollutant above a new limit -- between 50 and 100 parts per billion over one hour -- no longer would be acceptable.

The EPA also proposed more monitoring and better ways to alert the public about short-term high levels of sulfur dioxide. The new rules will become final by June 2.

The EPA estimated that if the rule were put in place with the strongest limits the agency is recommending, the benefits in 2020 would include 4,700 to 12,000 fewer premature deaths a year and 3.6 million fewer cases of worsened asthma. It also calculated that the costs of $1.8 billion to $6.8 billion would be greatly outweighed by the health benefits from such factors as fewer emergency room visits or lost days of work.

The University of Buffalo's Dr. Lockwood is lead author of a new report by Physicians for Social Responsibility that looks at the health impacts of coal from mining and transportation to burning it and handling post-combustion waste.

The report, released on Nov. 18, examines peer-reviewed scientific reports on the harm from all forms of coal pollution to the lungs, heart and nervous system.

The report also listed dangers to human health from climate change, including deaths in more frequent heat waves and the spread of infectious diseases such as malaria and dengue fever. Physicians for Social Responsibility won the 1985 Nobel Peace Prize for pressing for an end to the nuclear arms race. The advocacy group now also urges governments to adopt policies to reverse global warming and protect the environment from pollution.

The EPA's new rule on sulfur dioxide will make a difference especially for people who live near or downwind from the plants, said American Lung Association Vice President Janice Nolen. With sulfur dioxide pollution, even healthy adults who work or exercise outside may be at risk of harm, Ms. Nolen said.

John Kinsman, senior director for environment at the Edison Electric Institute, which represents investor-owned electric companies, said in a statement that the means of controlling sulfur dioxide would be worked out by 2014 on the basis of state plans. "It's far too early to know just what would be required of utilities to help meet a new standard," he said.

Electricity generation from fossil fuels, mainly coal, increased 70 percent between 1980 and 2008, and utilities reduced sulfur dioxide emissions by 56 percent in that period, Mr. Kinsman said.

That decline was based on the EPA's first sulfur reduction standards from 1971 and the acid rain reduction program of the 1990s. Utilities did it by placing scrubbers on some smokestacks and switching to low-sulfur coal.

Washington correspondent Daniel Malloy writes the "Pittsburgh On The Potomac" blog exclusively at PG+, a members-only web site of the Pittsburgh Post-Gazette. Our introduction to PG+ gives you all the details.