By Emily Flitter

NEW YORK (Reuters) - Environmental and public health groups asked a U.S. Appeals Court in a lawsuit filed on Wednesday to force the U.S. Environmental Protection Agency to reverse its decision to delay issuing a set of smog cleanup rules.

The groups, including the Natural Resources Defense Council and Earthjustice, argued the agency's June 6 announcement that it would wait to identify areas of the country where smog pollution is especially heavy until it gathered more information and reviewed existing pollution standards was illegal.

At issue in the lawsuit is a provision in the Clean Air Act that requires the EPA to decide what levels of smog pollution are acceptable, then identify parts of the country where pollution exceeds those levels and enforce their cleanup. The agency released standards and designations in 2008 and 2015, and was due to update them this year.

"Simply put, delay of designations delays the stronger pollution controls Congress mandated to protect people in communities with unhealthy air," said the lawsuit, filed in the U.S. Court of Appeals for the District of Columbia Circuit.

Liz Bowman, a spokeswoman for the EPA said the agency had asked lawyers representing the groups in a phone call on Tuesday to delay filing their suit for two weeks. She said the EPA was still working on the designations and its lawyers believed the suit would be unnecessary once the groups saw the results of the agency's work.

Bowman said the groups were reading too much into the delay. "The agency was not going to meet the original deadline for all 50 states," she said. "This administrator doesn't like being outside the bounds of statutory deadlines so he said extend it. We're continuing our work."

The topic has been a recent source of dispute. Environmental groups and representatives of industries that contribute to smog, like power plants, sparred in court over whether the previous designations were too lax or too strict.

Mustafa Ali, a former assistant associate administrator for environmental justice at the EPA, criticized the delay and said the suit, in which he was not involved, was warranted. If the EPA needed more time to deal with certain states over their designations, the agency could do so without the overall delay, he said.

"You can always work with states that are not moving quickly, you can build some accommodation into the process," he said.

"How long do these communities need to wait? What we're really doing is playing with their lives."

(Reporting by Emily Flitter; Editing by Tom Brown)