In this Nov. 10, 2010 file photo, oil refineries are shown in Deer Park, Texas. Under new EPA rules, some oil refiners, manufacturers and other operations will have to invest in pollution abatement upgrades. (David J. Phillip/AP)

The Environmental Protection Agency announced Friday that it will tighten the nation’s soot standards, a move that could help deliver major health benefits by the end of the decade but force some oil refiners, manufacturers and other operations to invest in expensive pollution-abatement upgrades.

Particles measuring less than 2.5 micrometers in diameter, also known as fine particles or soot, are possibly the most deadly widespread air pollutant. Measuring one-thirtieth the width of a human hair, these particles come from activities ranging from wood burning to vehicle emissions and can cause respiratory and heart ailments by entering the lungs and bloodstream.

Facing a court-ordered deadline of midnight Thursday, Assistant Administrator for the Office of Air and Radiation Gina McCarthy told reporters in a news call that EPA has proposed tightening the annual exposure to fine-particle soot from 15 micrograms per cubic meter of air to between 12 and 13 micrograms per cubic meter of air. Industry officials and environmentalists said the proposal, which will be finalized by mid-December, would have implications for both the U.S. economy and public health.

McCarthy called fine particles “a serious pollutant with serious consequences.” She said EPA estimates that the new rule would produce $30 to $86 in benefits for every dollar invested in pollution control.

But McCarthy added that the agency is prohibited from considering costs when determining soot concentrations. “For the standard setting, we rely on the science,” she said.

Paul Cort, the Earthjustice attorney who represented the Lung Association and the National Parks Conservation Association in a lawsuit forcing EPA to issue the rule, called the proposal an “opening offer” and vowed to press for more stringent restrictions.

“There’s no question that EPA’s proposal is going to save lives,” Court said, estimating that cutting exposure to 13 micrograms per cubic meter would avoid 8,000 premature deaths a year. But he added that reducing the concentration to 11 micrograms would boost that number to 27,000 avoided deaths.

Jeffrey R. Holmstead, head of the EPA’s air and radiation office under President George W. Bush, said he’s been “a little surprised” that industry hasn’t launched as hard a fight against this proposal as it did against an EPA smog proposal last year, which President Obama pulled back in September.

McCarthy said two of the rules that the EPA has finalized — including one curbing mercury and air toxins and another limiting sulfur dioxide and nitrogen oxide from sources such as power plants and cement plants — ensures that the tighter rule will only affect a tiny number of communities which face challenges such as old diesel engines around ports or railyards, or woodstoves in valleys.

“We’re already on the path for 99 percent of counties to meet the standard, without the need for additional state or local action,” she said.

EPA projects that as many as six counties will not to meet the standards by 2020, when counties must be in compliance, McCarthy said. They are Riverside and San Bernadino in California; Santa Cruz, Ariz.; Wayne County, Mich.; Jefferson County, Ala.; and Lincoln County, Mont.

The question of how to set an acceptable level of soot exposure has been the subject of political and legal wrangling for years. In 2006, the Bush administration rejected the advice of its Clean Air Scientific Advisory Committee to make the annual standard more stringent, and kept it at 15 micrograms per cubic meter, although it strengthened the 24-hour standard from 65 to 35 micrograms. Several states and environmental groups challenged the 2006 standards in court, and in 2009, a federal appeals court ordered the EPA to rewrite the rule.

The EPA’s staff and the Clean Air Scientific Advisory Committee, an independent group of experts, concluded that there is enough scientific evidence to lower annual average soot exposure to between 11 and 13 micrograms per cubic meter.

On June 6, Judge Robert Wilkins of the U.S. District Court for the District of Columbia ordered EPA to issue its proposed rule by June 14.

Holmstead said it would be a rush for the agency to finalize such an important rule within six months, by Dec. 14. “It’s not surprising to see another sweetheart deal between the Obama EPA and the environmental community,” he said. “It will ensure that the final rule comes out after the election but before a possible change in administrations.”

Court, however, questioned that assessment. “Believe me, they were not looking for this deal,” Court said. “This was thrust upon them, and now that they have it, they are claiming ownership.”

Once a rule is finalized, the EPA must determine how many counties across the country will be out of compliance with the new soot standards, and those communities must eventually cut down on pollution or risk losing federal funds.

Howard Feldman, director of regulatory and scientific affairs for the American Petroleum Institute, said a more stringent rule will discourage economic investment in counties that fail to meet federal air-quality standards.

“It’s in our interest to have a vibrant domestic economy,” Feldman said, adding that many companies eyeing a place to build a plant or refinery “perceive ­non-attainment to be non-investment.”

S. William Becker, executive director for the National Association of Clean Air Agencies, said that “there is going to be a significant workload” for some counties to meet the new standard.

“That’s no reason not to support and follow the science, but it’s one reason EPA and Congress will need to step up and provide additional resources and set strong federal control measures,” Becker said.

In the past week, GOP lawmakers and industry officials have lobbied the White House to keep the existing annual soot exposure standard in place, or at least allow the EPA to take comments on that option as part of its proposed rule.

“Our position is, look, everyone will take comments and let the chips fall where they may,” said Joseph Stanko, who heads government relations at the law firm Hunton and Williams and represents several utilities.

House Energy and Commerce Committee Chairman Fred Upton (R-Mich.) and Republican Reps. Ed Whitfield (Ky.) and Joe Barton (Tex.) sent a letter to EPA Administrator Lisa P. Jackson on June 6 arguing that scientific uncertainty still exists when it comes to reducing fine-particle pollution further.

Critics such as Feldman questioned the benefit of setting stricter standards for fine-particle pollution, which is already on the decline, because it contributes to mortality rather than causes it. “Neither you nor I know anyone who has died from PM 2.5 pollution,” he said, referring to the fine particle unit of measurement.

But Jonathan M. Samet, a pulmonary physician who directs the University of Southern California Institute for Global Health and chairs the EPA’s independent scientific advisory panel, said the scientific literature suggests that there are adverse health effects from soot pollution “at the higher-end of levels” that some Americans are exposed to right now, and the EPA administrator must adopt rules that ensure “an adequate margin of safety.”

When looking at the causes of premature death in the United States, Samet added, “particulate matter would be at the top of the list.”