WASHINGTON -- A proposal to boost auto sales by offering government-funded discounts to consumers who trade in old cars for new, more efficient models got a boost Wednesday from House Speaker Nancy Pelosi. But the proposal, which also is supported by Detroit auto makers and the United Auto Workers, is coming under fire from some foreign auto makers critical of a provision limiting the vouchers to vehicles built in North America. That limitation would exclude some of the most fuel-efficient cars and trucks sold in the U.S., including the Prius from Toyota Motor Corp. A bill introduced Tuesday by Rep....