California’s plant to drastically cut greenhouse gas emissions has automakers crying foul, claiming the move will increase car costs by hundreds of dollars. The Alliance for Automobile Manufacturers, an industry lobbying group, described the ambitious plan by California officials as a back-door attempt to regulate fuel economy. General Motors Corp., Ford Motor Co. and other automakers contend only the federal government has authority to enact fuel economy rules. The California Air Resources Board held its first public hearing Wednesday on the plan to reduce greenhouse gas emissions, which would require a 30 percent improvement in fuel economy of new cars and trucks in the coming decade. Other states can use either federal clean-air regulations or adopt the California standards. New York and other Eastern states, under pressure to meet federal clean-air requirements, have routinely adopted California rules. California represents 11.5 percent of the U.S. new car and truck market, according to the California Motor Car Dealers Association. The Air Resources Board estimated the regulations will add $241 U.S. to the cost of a typical passenger car by 2011 and $539 U.S. by 2014. For a large pickup or SUV, the estimated added cost will be $326 U.S. by 2011 and $851 U.S. by 2014. The Air Resources Board is expected to vote on the proposed regulations in September. By law, the rules have to be finalized by January 1. Automakers will be required to make changes beginning with the 2009 model year.