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WASHINGTON — The Trump administration on Thursday put forth its long-awaited proposal to freeze antipollution and fuel-efficiency standards for cars, significantly weakening one of President Barack Obama’s signature policies to combat global warming.

The proposed new rules would also challenge the right of states, California in particular, to set their own, more stringent tailpipe pollution standards. That would set the stage for a legal clash that could ultimately split the nation’s auto market in two.

The administration’s plans immediately faced opposition from an unusual mix of critics — including not only environmentalists and consumer groups but auto-industry representatives as well as individual states — who are now launching efforts to change the plan before it is finalized.