Legal Battle Begins Over Obama Bid to Curb Greenhouse Gases

WASHINGTON — President Obama’s most far-reaching regulation to slow climate change will have its first day in court on Thursday, the beginning of what is expected to be a multiyear legal battle over the policy that Mr. Obama hopes to leave as his signature environmental achievement.

In two separate but related cases to be jointly argued in the United States Court of Appeals for the District of Columbia Circuit, the country’s two largest coal companies, along with 14 coal-producing states, have challenged a proposed Environmental Protection Agency regulation, which the agency issued under the authority of the Clean Air Act, to curb planet-warming carbon pollution from coal-fired power plants. If put in effect as E.P.A. officials have proposed, the rule is intended to fundamentally transform the nation’s power sector, shuttering hundreds of coal plants and expanding renewable energy sources such as wind and solar.

Thirteen states and the District of Columbia are backing the Obama administration’s proposal. No matter the outcome of the case, it is widely expected that it will be appealed, and that more lawsuits will follow — and that its fate will ultimately end up before the Supreme Court.

In the two cases, Murray Energy v. E.P.A. and West Virginia v. E.P.A., the plaintiffs contend that the E.P.A. lacks the authority to issue the rule in the first place, and so should stop working on the rule before making it final.

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

Legal experts say it is also possible that the judges could throw the case out, since the rule has only been proposed and thus contains language that could change when released in the final form.

“Is industry right that the agency lacks the authority to regulate? The challenge is extremely unusual, since the rule is proposed, and not final,” said Jody Freeman, the director of Harvard University’s environmental law program and a former senior counselor to Mr. Obama. “For a court to entertain that would go against decades and decades of precedent.”

If the court does entertain the case, it will enter into more unusual legal territory. The coal companies and the E.P.A. dispute the interpretation of ambiguously worded amendments to the Clean Air Act passed in 1990. Under those amendments, legal experts say, it is not clear whether the E.P.A. has the authority to use one section of the Clean Air Act to regulate greenhouse gas pollution from power plants, since the agency has already used a different section of the law to regulate different pollutants from power plants.

When the 1990 legislation was passed, the House version of the law appeared to prohibit such “double regulation,” experts say, but the Senate version appeared to allow it. The final version of the legislation left the question unclear.

In arguing that it has the authority to regulate different pollutants from the same sources, the E.P.A. will point to the 1990 Senate language. In arguing that the agency lacks the authority, the coal companies will point to the House language.

“It’s an extremely technical argument about how the statute was put into the U.S. code 25 years ago — it’s basically a clerical error,” said Kevin Desharnais, an expert on environmental law with the firm Mayer Brown.

Patrick Morrissey, attorney general of West Virginia, which is leading the states’ petition against the E.P.A., said the agency is trying to exploit the ambiguity in a law to enact sweeping regulations that could transform the American energy economy. “They are trying to bring life to a clerical error,” he said. “Now it’s being used to put forth a major transformation to American energy policy — and to cause harm to West Virginia.”

Opponents of the rule say they are optimistic about the outcome in part because of the judges presiding over the case. All three were appointed by Republican presidents — two by President George W. Bush, and one by his father.

Typically, a rule is proposed by the E.P.A., which then takes public comment on the proposal. The E.P.A. may then adapt the rule before issuing the final version. The Obama administration proposed the coal plant rule last June, and is expected to release the final version this summer.