Updated from 12:09 p.m. EDTAs General Motors ( GM) revises its restructuring plan, a bankruptcy filing is "probable" but not preferred, CEO Fritz Henderson said Friday. "Our preference is to accomplish this outside of a bankruptcy, but I would say the overriding preference is to accomplish our goal" of restructuring quickly, Henderson said on a conference call with reporters. "It's pretty simple," he said. "If we can't accomplish it outside of bankruptcy by June 1, we will do it inside of bankruptcy." He said GM is operating on two tracks, preparing for both bankruptcy and out-of-bankruptcy operations, but the two strategies have various similarities. GM has already received $13.4 billion in government aid, and it must meet strict government requirements to cut labor costs and debt by a June 1 deadline. Henderson said additional money will be needed during the current quarter. In the closing days of the Bush administration, GM said it would need $18 million in federal loans this year, and Henderson said nothing Friday to counter the suggestion that the remaining $4.6 billion would be sought by the end of the quarter. Henderson dismissed speculation that two brands, GMC and Pontiac, could be shut down. He said GM remains committed to a "four core-brand strategy" that includes Buick, Cadillac, Chevrolet and GMC, "the bulwark of our strategy going forward." Pontiac has been slated to remain as a niche brand. "I don't always believe everything I read," Henderson said. "Our four core-brand strategy is the right way to go to market."