By Kevin Krolicki DETROIT (Reuters) - The U.S. auto industry needs $50 billion in low-interest, government-guaranteed loans and could return to the U.S. Congress for a second round of $25 billion after approval of the first $25 billion, the head of the United Auto Workers union said on Tuesday. UAW President Ron Gettelfinger, speaking at the Reuters Autos Summit in Detroit, said it was critical for U.S. lawmakers to pass funding for the loan program quickly. The federal loan program has run into some opposition from critics, who call it a bailout for the auto industry. But Gettelfinger said federal loan guarantees would help the auto industry make new investment in fuel-saving technology and preserve jobs at a time when auto sales are slumping and credit markets are tight. The industry could still secure funding for up to $50 billion in two installments, he said. Automakers had initially looked to secure that much in loans before scaling back their request in the interest of securing the $25 billion included in a 2007 energy bill. 'There's always that possibility,' he said of a second round of loans. 'When people see the success of it -- what it means for the industry, to the country, to the environment, to the consumer -- I think it will be easier the next time around.' Lawmakers must appropriate about $7.5 billion to cover default risk in order to issue the loans. The $25 billion was pledged to the auto industry to help cover the cost of meeting fuel economy standards that will be raised to 35 miles per gallon on average starting in 2020. With U.S. auto sales near 15-year lows and no expectation of a quick turnaround for the world's largest auto market, General Motors Corp(GM.N: Quote, , Research, ), Ford Motor Co(F.N: Quote, , Research, ) and privately held Chrysler LLC have faced pressure to shore up cash to ride out the downturn.