WASHINGTON, Dec 10 (Reuters) - U.S. Supreme Court justices offered President Barack Obama's administration some encouragement on Tuesday as it weighed the lawfulness of a major federal air pollution rule regulating emissions that cross state lines.
Although it was unclear how the court would rule, a majority of the eight justices hearing the case at points in the 90-minute argument voiced some support for the regulation, which has been challenged by some states and industry groups.
The government is defending a regulation that had been due to go in effect in January 2012. The ninth justice, Samuel Alito, recused himself from the case for undisclosed reasons.
The regulation, which requires 28 states in the eastern part of the country to reduce emissions of sulfur dioxide and nitrogen oxides, was put on hold while courts weighed the challenges.
Among the challengers are Entergy Corp, Luminant Holding Company and the United Mineworkers of America.
In striking down the rule in an August 2012 ruling, the U.S. Court of Appeals for the District of Columbia Circuit wrote in part that the U.S. Environmental Protection Agency could not impose a federal plan on a state until the state was given notice of the amount of pollution it emitted that makes it more difficult for other states, downwind, to meet government-set air quality standards.
The appeals court also found that EPA authority was limited over what factors it could consider when setting targets for the states.
The Obama administration appealed the decision, which focused on whether the EPA exceeded its authority under the Clean Air Act, to the Supreme Court.
Both Chief Justice John Roberts and Justice Anthony Kennedy, two members of the conservative wing of the court, offered some encouragement to the administration.
During one exchange with Peter Keisler, a lawyer representing business interests challenging the EPA rule, Kennedy seemed to suggest he might support the administration's argument that it could consider cost-effectiveness when determining what emissions reduction goals a state should face.
In a similar vein, Roberts challenged Jonathan Mitchell, a lawyer representing Texas and other states that object to the regulation.
Mitchell said the EPA had "left states completely in the dark" about what their obligations were.
Although the states might have a hard time with the process, "it's what the statute says," Roberts responded.
Throughout the argument, the liberal members of the bench stressed that states could still have a say in the process even after EPA has told them what their targets should be. Under the Clean Air Act, states can make a counter-proposal at a later date, Justice Elena Kagan and others pointed out.
A ruling for the EPA would not be "the end of the game," she said.
A ruling is expected by the end of June. The two consolidated cases are EPA v. EME Homer City Generation and American Lung Association v. EME Homer City Generation, U.S. Supreme Court, 12-1182 and 11-1183.
(Reporting by Lawrence Hurley; Editing by Howard Goller and Leslie Adler)