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WASHINGTON — The Trump administration, setting the stage to move forward with one of its most consequential climate-policy rollbacks, announced Thursday that it had decided to scrap negotiations with California over the president’s plan to undo Obama-era fuel efficiency standards for c ars and light trucks .

The move makes a protracted legal battle almost certain. At the heart of the talks was California’s longstanding right to opt out of national auto emissions rules and set its own tailpipe standards. State officials have vowed to sue to protect that authority if the administration tries to impose weaker federal standards on California and the dozen states that follow its lead.

Xavier Becerra, the California attorney general, said Thursday the state was “prepared to defend our national Clean Car standards even if the Trump administration intends to go AWOL.”

Under rules established by President Barack Obama’s administration to cut planet-warming greenhouse gas emissions from tailpipes, national fuel economy standards would nearly double by 2025. The Trump administration said in August that it intended to freeze that measure after 2021, when new cars must average around 30 miles a gallon. It also said it would challenge the right of California and the states that follow its lead to set their own rules.