. . . . "The auto industry is part of the backbone of the U.S. economy.''The low-interest loans, at rates of about 4 percent to 5 percent, would pay for up to 30 percent of the cost of retooling plants to build hybrids, plug-in hybrids, electric cars and other alternatives.Ford and General Motors Corp.'s credit ratings have fallen below investment grade, making it difficult for the companies to borrow mone" .