General Motors Corp. could be majority owned by the federal government and the United Auto Workers under a massive restructuring plan laid out Monday that will cut 21,000 US factory jobs by next year and phase out the storied Pontiac brand. The plan, which includes an offer to swap roughly $27 billion in bond debt for GM stock, would leave current shareholders holding just 1 percent of the century-old company, which is fighting for its life in the worst auto sales climate in 27 years. GM is living on $15.4 billion in government loans and faces a June 1 deadline to restructure and get more government money. If the restructuring doesn't satisfy the government, the struggling company could go into bankruptcy protection. GM said in a filing with the US Securities and Exchange Commission that it will ask the government to take more than 50 percent of its common stock in exchange for canceling half the government loans to the company as of June 1. The swap would cancel about $10 billion in government debt. In addition, GM is offering the UAW stock for at least 50 percent of the $20 billion the company must pay into a union run trust that will take over retiree health care expenses starting next year.