The U.S. auto industry is expected to record its fourth best year ever when automakers release December vehicle sales on Jan. 3. But the results are bittersweet for Detroit's automakers as they continue to cede market share and see profits crimped by lucrative rebates, according to the Detroit News. December sales are expected to exceed those of a year ago as much as 3 percent. They should also end a two-month slide in sales thanks to an advertising blitz that lured buyers with cash-back offers and low-rate financing deals, the Newssaid. "The incentives were very, very aggressive with all the cars," said Frank Ursomarso Sr., a multi-franchise dealer based in Wilmington, Del. "We were up 23 percent over last December, which was quite a big gain considering that last December was pretty good, too."  A strong final month should help lift 2002 vehicle sales to at least 16.6 million units, industry experts forecast. While that is down about 3 percent from last year's 17.2 million, it is still considered a strong, above-average performance, the News said. But the future is cloudy.  Industry officials and analysts are predicting a disappointing 2003, with annual sales expected to be between 15.8 million to 16.5 million units, according to the News.