Refiners said it could raise the price of a gallon by 6 to 8 cents, but clean-air groups said it would be more like 1 cent. The difference depends in part on details of the rule that have not been made public.

News of the proposal was first reported by The Washington Post on its Web site.

Gasoline in the other 49 states can now have up to 30 parts of sulfur per million, and the proposed rule will be 10. The main problem is that at the current level, sulfur reduces the effectiveness of the catalytic converter, which eliminates nitrogen oxides, hydrocarbons and carbon monoxide.

Charles T. Drevna, president of the American Fuel and Petrochemical Manufacturers, the refiners’ main trade association, said the companies had in the last few years cut the sulfur content by 90 percent, to 30 parts from 300 parts, at a cost of $10 billion in capital improvements. He said that the proposed cut would cost another $10 billion. Because the process consumes energy, it will raise the carbon dioxide output of refineries.

Mr. Drevna said that the E.P.A. had not demonstrated that the cut was needed to meet existing air quality standards. He said he was hoping the industry would have time to respond.

But Mr. Becker said that when put in place, the rule would cut nitrogen oxide emissions by 260,000 tons, compared with about 10 million tons from all mobile sources. That is the equivalent of 33 million cars, he said.