The head of the Environmental Protection Agency tightened the nationwide limit on ozone, or smog, Wednesday, but the decision pleased neither medical experts who wanted stronger action nor industry officials who wanted no change. 

EPA Administrator Stephen Johnson's long-awaited decision will almost certainly force further pollution reductions in the three dozen metro areas that already violate the current ozone limit, including Dallas-Fort Worth. It also will require pollution cuts for the first time in some areas where the air had been considered clean, though new violation areas will not be listed until 2010.

The types of reductions necessary, as well as the time allowed for making them, will vary – from three years for marginal violators to 20 years for the worst, such as Los Angeles. The EPA has not determined what cuts might be needed, but in general, vehicles and industries will have to reduce pollution.

Mr. Johnson set the new ozone limit at 75 parts per billion, rejecting the recommendation of the EPA's independent science advisers. The science panel, drawn from universities and research labs, unanimously called for a new ozone limit no higher than 70 ppb and as low as 60.

Medical groups across the country endorsed that view, saying deep ozone cuts were vital to protecting people's lungs and lives.

Industries and others – including Gov. Rick Perry and Texas' state environmental agency – urged Mr. Johnson to keep the current standard of 80 ppb. They said further cuts in smog would sap the economy while yielding no significant health benefits.

Either health groups or industries could challenge the decision in federal court. The last time an EPA administrator tightened the ozone limit, in 1997, industry lawsuits delayed the new standard's implementation for four years. The Supreme Court unanimously rejected the industry challenges in 2001.

Heavy campaigning

During recent months, supporters and opponents of a stricter standard heavily lobbied the EPA and the White House's Office of Management and Budget, organizing letter-writing campaigns and pressing Bush administration officials in person.

Mr. Johnson said he based his decision on science alone, noting that the Clean Air Act forbids the EPA from considering costs in setting the limits on key pollutants – a position that the Supreme Court reinforced. Mr. Johnson said Wednesday that he now wants Congress to let future administrators consider economic factors. Whether Congress would agree to that change is unclear.

Memos show that political tension between the EPA and the White House continued until the last moment and forced the environmental agency to back off on at least one aspect of its proposal. Still, Mr. Johnson credited President Bush with cleaning up the nation's air.

"America's air is cleaner today than it was a generation ago," Mr. Johnson said. "By meeting the requirement of the Clean Air Act and strengthening the national standard for ozone, President Bush and [the] EPA are keeping our clean air progress moving forward."

Environmental groups blasted the new standard as inadequate.

"Once again, the Bush administration has chosen to disregard the advice of the EPA's own independent science advisers," said Frank O'Donnell, president of Clean Air Watch, a Washington, D.C-based advocate group. "Unfortunately, science appears to have been tainted by political science. The Bush administration is compromising public health to save industry money."

Industry groups were equally unhappy.

"The costs are too high and the benefits too unclear to impose this new burden on America's manufacturers and employees," said John Engler, president of the National Association of Manufacturers. "Anyone interested in preserving high-paying U.S. jobs in manufacturing and keeping a lid on energy prices should be disappointed by today's ruling."

High levels

Ozone, a main component of smog, is a powerful irritant that damages lungs, causes breathing problems and asthma attacks, and harms plants and wildlife. It forms in the summer when the sun cooks emissions from vehicles, diesel equipment, industrial plants and other sources.

All nine North Texas monitors that track the region's compliance recorded ozone levels higher than the existing federal limit in 2005 and 2006; five of nine were over the limit in 2007. Figures for 2008 aren't available yet.

Even with some new anti-smog measures, most of the monitors would still record more than the current limit in 2009, according to projections in the state's most recent smog plan. The EPA is reviewing that plan and possible revisions with the Texas Commission on Environmental Quality.

In November, a Dallas Morning News analysis found that even with every pollution-cutting strategy proposed so far, all of North Texas monitors would be far higher than any anticipated new limit.

Texas' top officials joined the industries in opposing a lower ozone limit. Mr. Perry was one of 11 governors who signed a Dec. 11 letter to Mr. Johnson asking him to keep the current standard in place. The chairman of the Texas Commission on Environmental Quality also endorsed the campaign against a lower limit.

Local officials contend that the state and the EPA haven't given them enough tools to solve local smog problems. Vehicles are the biggest North Texas polluters, with industries second. Local clean-air planners frequently complain that they cannot do anything about the top local pollution source because auto standards are a federal matter.

"The EPA says, 'You come up with a plan to tell us how you're going to attain a standard, but by the way, we're not going to let you control 75 percent of the pie,' " said Laura Fiffick, the city of Dallas' environmental director and a member of the EPA's Local Government Advisory Committee.

Local officials in Dallas-Fort Worth also were unhappy with being shut out of the writing of the latest state smog proposal, called a state implementation plan, or SIP.

"We really had no recourse," Ms. Fiffick said.

Another concern for North Texas smog-fighters is the amount of ozone blowing in from other areas.

"We've got pollution blowing in here, just as our pollution is blowing out of our area" and worsening smog in downwind areas, mostly to the north, said Mike Eastland, executive director of the North Central Texas Council of Governments.

"To pick out six or seven counties and tell them, 'You do these things in your geographic area,' well, we're beyond that. When you get down to a standard this low, it's going to take everybody pitching in."