“Looking at it now, it seems they were more interested in stalling the progress of the conversation than actually working to make a deal,” Ms. Gunasekara said.
The decision to abandon talks does not necessarily mean that a final proposal from the administration is imminent. The E.P.A. had planned to complete the rollback proposal by the end of March, but the partial government shutdown early this year set that target back to May or June, agency officials said.
Automakers, who fear that competing rules will bring chaos to the domestic auto industry, called for continued talks.
“We continue to believe there is a middle-ground solution that supports the goals of the administration, state of California, as well as automakers,” said John Bozzella, chief executive of Global Automakers, which represents automakers and parts suppliers with operations in the United States.
“We always knew achieving one national program would be challenging,” said Gloria Bergquist, a vice president at the Alliance of Automobile Manufacturers, which represents the country’s biggest automakers. But a compromise “is worth striving for,” she said. “We encourage everyone to keep focusing on how we get there.”
The announcement comes amid fast-deteriorating relations between Washington and California.
In recent weeks the Trump administration has said it was terminating a $929 million federal grant for the state’s struggling high-speed rail project, and the Transportation Department said it was exploring legal options to claw back $2.5 billion that had already been spent. President Trump has also threatened to cut off federal funding for wildfire relief after devastating blazes that killed 89 people.
Mr. Trump also lashed out on Twitter when 16 states sued over his decision to declare a national emergency in order to obtain funding for a border wall, writing that California, “the state that has wasted billions of dollars on their out of control Fast Train, with no hope of completion, seems in charge!”
Lisa Friedman reported from Washington and Hiroko Tabuchi from New York.
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