The Trump administration is expected to begin rolling back stringent federal regulations on vehicle pollution that contributes to global warming, according to people familiar with the matter, essentially marking a U-turn to efforts to force the American auto industry to produce more electric cars . The announcement — which is expected as soon as Tuesday and will be made jointly by the Environmental Protection Agency administrator, Scott Pruitt, and the transportation secretary, Elaine L. Chao — will immediately start to undo one of former President Barack Obama’s most significant environmental legacies.