He added, “There are ongoing harms incurred by the states which cannot be adequately addressed.”

Judge Kavanaugh, noting that the E.P.A. has said it intends to revise the rule before releasing a final version, said: “Maybe they’ll still tweak it. For us to get in the middle of it before it happens seems highly unusual.”

Judge Kavanaugh also appeared skeptical of the argument that preparations could harm states in the handful of months before the rule is expected to be finalized this summer. “It could take as much time for us to write this opinion as it will for E.P.A. to release the final rule,” he said.

Among the lawyers arguing on behalf of the coal companies was Laurence H. Tribe, a well-known Harvard scholar of constitutional law who was a mentor to Mr. Obama when he attended law school. Republicans who oppose the rule have cheered Mr. Tribe’s role in the case.

In court on Thursday, Mr. Tribe laid out a broad, sweeping argument against the rule as unconstitutional, echoing spirited arguments that he has been making for months in legal briefs, congressional testimony and an opinion article in The Wall Street Journal.

By requiring states to enact new policies to change their energy economies, Mr. Tribe told the court, “the E.P.A. is coloring outside the lines. They’re trying to make law, not execute law. They are commandeering the states.”

“States are not to be treated as puppets,” he added.

Mr. Tribe also engaged in the narrow legal argument over two ambiguously worded amendments to the 1990 Clean Air Act that is at the heart of the dispute between the E.P.A. and the coal companies.

Under those amendments, legal experts say, it is not clear whether the agency has the authority to use one section of the Clean Air Act to regulate greenhouse gas pollution from power plants when it has already used a different section of the law to regulate other kinds of pollutants from the plants.