The U.S. government is proposing new air quality standards to lower the amount of soot that can be released into the air.

The move, announced Friday, is likely to win support from environmental groups and public health advocates but exposes the president to potential criticism from Republicans and industry officials that the rules are overly strict and could hurt economic growth.

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A device is used to measure the amount of diesel particulate pollution emitted by a school bus lacking pollution control devices on its exhaust system and on its engine before stricter air quality standards were proposed. (Bob Child/Associated Press)

Perhaps wary of the rule's political risk, the Obama administration had sought to delay the new soot standards until after the November presidential elections. But a federal judge ordered officials to act after 11 states filed a lawsuit seeking a decision this year by the U.S. environmental agency.

An administration official said the new rule was based on a rigorous scientific review. Virtually all counties in the United States would meet the proposed standard with no additional actions needed beyond compliance with current and impending rules set by the Environmental Protection Agency, the official said.

Administration officials described the rule to The Associated Press on condition of anonymity because it has yet to be announced.

Soot is made up of microscopic particles less than 2.5 micrometers in diameter that are released from smokestacks, diesel trucks and buses, wood-burning stoves and other sources, contributes to haze and can burrow into lungs. Breathing in soot can cause lung and heart problems.

Eleven states, including New York and California, filed suit earlier this year to force a decision. The states and the American Lung Association say current standards jeopardize public health.

Dr. Albert Rizzo, chairman of the board of the American Lung Association, said soot, also known as fine particle pollution, is a known killer.   

"The science is clear, and overwhelming evidence shows that particle pollution at levels currently labeled as officially 'safe' causes heart attacks, strokes and asthma attacks," he said.

Soot has been linked to thousands of premature deaths each year, as well as aggravation of respiratory illnesses, heart attacks and strokes.

More than a dozen states, along with environmental groups, sued the EPA several years ago, contending that the Bush administration had ignored science and its own experts when it decided in 2006 not to lower the nearly decade-old annual standard for soot. The agency's own analysis found a lower standard recommended by scientific advisers would have prevented almost 2,000 premature deaths each year.

The new rule would set the maximum allowable standard for soot in a range of 12 to 13 micrograms per cubic meter of air. The current annual standard is 15 micrograms per cubic meter.

Canada and the United States have completed a joint transboundary report on particulate matter to support an air quality agreement, according to Environment Canada's website.

On Tuesday, the World Health Organization declared that diesel exhaust causes cancer, a ruling that the agency said could make exhaust as important a public health threat as secondhand smoke.

With files from The Associated Press