By Valerie VolcoviciWASHINGTON (Reuters) - The Environmental Protection Agency is expected to propose on Wednesday more stringent air quality standards for ground-level ozone, the main culprit in smog, sources said.Under a court-ordered deadline of next Monday to release its proposal, the agency could propose a National Ambient Air Quality Standard between 65 and 70 parts per billion concentration of ozone, and take comment on standards within a 60-75 ppb range, sources familiar with the matter said.That would compare with the current level of 75 ppb set under then-President George W. Bush in 2008The EPA would have to finalize the rule by October 2015. The agency declined to commentThe proposal, which will apply not only to power plants but to cars and oil and gas facilities, is expected to face opposition from industry groups.The tougher standards would be closer to the proposal drafted in 2011 by former EPA Administrator Lisa Jackson, which was withdrawn by President Barack Obama before its release because of concerns about regulatory costs during a time of economic recovery.Although Obama had directed the EPA to come up with a new proposal, the agency did not take action, prompting the American Lung Association and green groups Earthjustice, the Sierra Club, the Environmental Defense Fund and the Natural Resources Defense Council to sue and get a court-ordered deadline.Health and environment groups say the new standards can lower the risk of early deaths, asthma and other respiratory illnesses from the pollutant."President Obama is not up for re-election. This should be a centerpiece of his environmental legacy," said Terry Maguire, the Sierra Club's Washington representative on smog pollution.He said the coalition of green and health groups had been pressing for a standard of 60 ppb, but added he could support a range of 60-70 ppb, which EPA scientists have recommended.For months, industry groups had been preparing for the release of a standard as low as 60 ppb, estimating a price tag of $270 billion a year, according to the National Association of Manufacturers.Howard Feldman, regulatory affairs director at the American Petroleum Institute, said air quality would continue to improve without regulatory change.Setting the standard at the level proposed by the EPA would make attainment "extremely difficult" for 94 percent of the country, Feldman said.(Reporting by Valerie Volcovici; Editing by Peter Cooney)Join the conversation about this story Click here to read full news..