A report by the National Academy of Sciences on possible increases to U.S. fuel economy standards due early this week has been revised to give automakers more time to improve fuel efficiency, a source familiar with the plans said on Friday. The report, still expected to offer a range of possible increases for fuel economy standards, avoids making a specific recommendation. Many studies on fuel economy have looked at increases possible in 10 years or more, giving automakers enough lead time to design and build more efficient engines and vehicles. The panel's report is now expected to offer a similiar time frame. The debate over the fuel economy has heated up this summer as environmental groups saw an opportunity to raise federal standards for the first time in years. Republican leaders who have traditionally helped automakers oppose such moves have also been more receptive to increases beyond the current 27.5 miles per gallon average for cars and 20.7 mpg for trucks. As part of his energy plan, President Bush has said his administration will use the panel's report as a starting point for considering higher standards. But the U.S. Congress has already begun debating whether to raise the standards, and a House committee has approved a bill calling for a slight increase. Detroit's Big Three, led by GM, have been staunchly against any increase in federal fuel economy standards, saying changes would imperil passenger safety and hurt the economy. GM has released a study saying any efforts to cut vehicle weight to meet higher fuel economy standards would increase the fatality risk in accidents. GM also said that a 3 mpg increase in truck standards would force GM to cut production by 1 million vehicles, slash jobs and close factories. The industry isn't united on the topic, however. On the other end, Honda Motor Co., Ltd., says higher standards are fine, but prefers the numbers to be set by government experts, rather than Congress.