WASHINGTON —  The Environmental Protection Agency on Thursday released an analysis of its new proposal to reduce smog levels that shows higher economic costs _ but potentially more lives saved _ the more stringent the regulation is.

The document angered environmentalists because in addition to analyzing three relatively stringent smog levels, EPA decided to study a fourth less-stringent smog level after intervention by the White House Office of Management and Budget, according to public documents in an EPA docket.

"The OMB ordered EPA to analyze a weaker standard than they had talked about earlier, and that to me is clear evidence that the White House is tampering with the EPA proposal and trying to make it weaker," said Frank O'Donnell, president of Clean Air Watch.

EPA spokeswoman Jennifer Wood countered that the exchange between EPA and the OMB was routine.

"It's standard practice for EPA to coordinate with our federal partners during any rulemaking," Wood said.

At issue is the EPA's June recommendation for the first new limits since 1997 on ground-level ozone, commonly known as smog.

EPA measures smog by the concentration of ozone molecules in the atmosphere over an eight-hour period. The current standard is .084 parts per million. EPA is proposing reducing that to somewhere between .070 and .075 parts per million.

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It is also accepting comments on leaving the level unchanged _ as favored by industry _ or reducing it to .060 parts per million _ a lower level advocated by environmentalists. The agency will settle on a final figure by March 12.

The document released Thursday was a "regulatory impact analysis" aiming to quantify costs and benefits. These were found to vary widely, and industry officials said this argued in favor of more study before taking action.

"If we're going to move forward with something so very expensive we think we need more certainty," said Bryan Brendle of the National Association of Manufacturers.

An early draft of the analysis shows EPA planned to analyze the impacts of lowering smog levels to .070, .075 or .065 parts per million. OMB recommended .079 parts per million to be considered, too, and EPA did so in the document released Thursday.

At the .065 parts per million level, findings ranged from economic costs of up to $46 billion in 2020 coupled with as few as 530 or as many as 2,400 premature deaths avoided per year. Reduction to .079 parts per million could cost up to $3.3 billion, and prevent 19 to 85 premature deaths each year.

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