GM Offers New Rebates: In an effort to boost its softening sales, General Motors began four new incentive programs, offering 4.9% short-term car loans on some top-selling models, such as the Corsica and Beretta. Analysts said the rebate programs would likely help improve March sales, which have lagged behind the strong pace of 1988. Ford and Chrysler also are offering 4.9% financing rates, but their programs are not as extensive. GM’s inventory of unsold cars at the end of February was estimated at 85 days, while Ford’s was 81 days and Chrysler’s 94 days. The industry considers a 65- to 70-day supply of cars acceptable.