EPA Regional Administrator Richard Greene signed off on the plan after a year of talks with the state's environmental agency, the Texas Commission on Environmental Quality. When the commission adopted the plan in May 2007, Mr. Greene said he would not approve it without changes.

Talks since then focused less on adding pollution-cutting measures to the plan than on whether the state's strategy was strong enough to meet federal requirements. State officials argued that the plan would yield better results than critics maintained, especially with new state money for voluntary pollution-cutting incentives.

In recent months, EPA officials have said the discussions convinced them that the plan was sufficient. Mr. Greene's approval comes with conditions that the state is working on meeting.

"Today represents a turning point," said Mr. Greene, who was making what could be his last major decision as the EPA's regional chief. The job is a political appointment typically filled by the president.

Mr. Greene, state environmental commission Chairman Buddy Garcia and a dozen local mayors, county judges and others held a news conference Tuesday afternoon in Arlington to announce the initial approval. After the EPA proposal is published in the Federal Register, the agency will take public comments for 30 days before making a final decision by year's end.

Absent from the 80-minute event at the North Central Texas Council of Governments' offices were any representatives of state and local environmental groups that have expressed strong disappointment with the plan.

"None of us had any knowledge of this" event, said Rita Beving, a clean-air advocate with the Dallas Sierra Club. The event was planned around the schedules of the 14 invited participants but was not announced to the public until Tuesday morning.

As recently as May 6, experts working with the environmental groups met with the EPA for several hours to air technical objections to the plan. "We tried to work with them in good faith, but they definitely failed us," Ms. Beving said.

Environmental and public health groups contend that the EPA should have stuck with its initial conclusion that the plan does not go far enough in reducing air pollution from vehicles, industries and other sources.

The EPA could have rejected the plan outright, forcing the state to redraft it. If that happened, however, administrative moves by the state might have postponed some clean-air measures for up to three years. "Delay, delay and delay," Mr. Greene said. "The time to move forward is now."

He said the EPA's discussions with the state environmental commission produced better estimates of how much pollution the plan would cut. The plan would order some new cuts in industrial emissions, but not as deep as environmentalists demanded.

Other major elements are voluntary, state-funded programs that help businesses replace old, dirty industrial diesel engines and low-income people replace older cars with newer, cleaner ones. The 2007 Legislature boosted funding for those programs and directed much of the money to the Dallas-Fort Worth area.

Mr. Garcia, the state environmental commission chairman, said those programs are rapidly producing benefits, including repair or replacement of nearly 15,000 older cars in urban North Texas.

"We've taken a good plan and made it better," he said.

But Dr. Al Armendariz, a Southern Methodist University environmental engineering professor who has done a technical analysis of the state's plan, said it is still fatally flawed. He predicted ozone levels would still exceed federal limits by the 2010 target date.

"They just recalculated the emissions and didn't put any new emissions reductions in the plan," Dr. Armendariz said. "That's what's so frustrating."

An outright rejection by the EPA would have sent a signal to Texas politicians and businesses that the agency is serious about requiring stronger clean-air measures, he said. "What is it that ... [the EPA] is really afraid of?"

Mr. Greene said he is confident that every area of North Texas would have cleaner air by 2010 under the state's plan.

Vehicles – including cars, trucks, buses and off-road equipment such as construction machinery and locomotives – are collectively the region's biggest polluters. Industries – such as the cement plants in Ellis County, factories across the region and fossil-fuel power plants across eastern Texas – are second.

Ozone, the chief component of smog, leads to a wide range of lung ailments. This spring, the EPA lowered the amount of ozone allowed in the air, although not as much as the agency's science advisers unanimously recommended. Texas environmental officials opposed the tighter ozone limits, saying that meeting them would cost too much.

The plan the EPA intends to approve would not lower ozone levels to the new, tighter federal limit. That standard will require a new round of plans and talks.

Arlington Mayor Robert Cluck, a physician, said local cooperation is helping clean up the air, but he emphasized that ozone levels that North Texas children are breathing are still unhealthy. He suggested that no amount of ozone might be safe for children.