WASHINGTON — California officials and clean air advocates are increasingly concerned the Trump administration may try to unravel a key program to drive down greenhouse gas emissions from automobile fleets while also jeopardizing the ability of California and other states to set pollution standards stronger than federal rules.

Backed by automakers, Trump officials are in talks with their California counterparts to weaken tough vehicle tailpipe standards approved by the Obama administration. The standards are aimed at reducing greenhouse gases, but could also help reduce emissions that cause smog and particulate pollution, and 13 other states have adopted them, including Washington, Pennsylvania and New York.

California has long enjoyed the authority to set pollution standards stronger than the federal government’s, a legacy of the state’s early battles against urban smog, which predated the 1970 Clean Air Act. But in testimony to a Senate committee last week, U.S. Environmental Protection Agency Administrator Scott Pruitt left open the possibility he might seek to revoke California’s authority.

“Federalism doesn’t mean that one state can dictate to the rest of the country,” Pruitt told the Senate Environmental and Public Works Committee. He then added that “we recognize California’s special status in the statute and we are working with them to find consensus around these issues.”

Three days after Pruitt’s comments, the chair of the California Air Resources Board issued her own warning shot against possible EPA intervention.

“I think there would be a war with many states lining up with California,” said CARB Chairwoman Mary Nichols, speaking at a Palo Alto, Calif., conference sponsored by Bloomberg New Energy Finance.

Nichols and other state officials note that the EPA, under the Obama administration, granted California a 2013 waiver to implement its own, tougher tailpipe standards. Never before has an EPA administrator tried to revoke a waiver previously granted to the state.

The administration plans to decide on future tailpipe emission standards by April 1.