The particles, 28 times smaller than the width of a human hair, are linked to premature death from heart and lung disease, as well as chronic bronchitis and asthma.

Action on particulates, which Leavitt puts at the top of his air quality agenda, is the next regulatory step after the EPA designated them as a pollutant in 1997.

"There is nothing we can accomplish that will increase the health of our air than decreasing concentrations of (particulate matter)," Leavitt told reporters.

The EPA action sets in motion a process where states must submit plans to reduce particulate emissions by early 2008, with compliance required in the 2010-2015 time frame.

Partial attainment of the standards in 2010 could prevent 15,000 premature deaths, according to agency analysis.

Tiny particles come from a wide array of sources ranging from cars and trucks to wood-burning stoves, forest fires, power plants and factories.

In Eastern states, the majority of the pollution comes from coal-burning power plants. In California, which has no coal facilities, most is from cars and trucks.

Environmentalists said EPA's rules won't lead to fast enough reductions in particulate emissions from the nation's 1,100 coal-burning power plants, the largest single source.

"EPA needs to take swift action to cut the dangerous pollution from power plant smokestacks or millions of Americans will be left gasping for clean air," said Vickie Patton, an attorney at Environmental Defense.

EPA's plan to cut utility emissions by 70 percent by 2015 will mark one of the most productive periods in U.S. air-quality improvements, Leavitt said.

"This is not about the air getting dirtier," Leavitt said. "It's about the air getting cleaner and our standards getting tougher."

There is no outright penalty for noncompliance, but states that fail to submit plans could lose federal transportation funds, Leavitt said.

State governors had asked EPA to designate 141 counties as non-compliant, far short of the 243 EPA named in a preliminary list it will finalize in November.

The EPA found non-compliant counties in the following states plus the District of Columbia: Alabama, California, Connecticut, Delaware, Georgia, Illinois, Indiana, Kentucky, Maryland, Michigan, Missouri, Montana, New Jersey, New York, North Carolina, Ohio, Pennsylvania, Tennessee, Virginia, West Virginia, and Wisconsin.