Updated from 3:24 p.m. ESTGeneral Motors ( GM) stunned the stock market Wednesday with an ominous profit warning, leading to speculation that the auto giant will be forced into a restructuring that could permanently alter the face of one of America's most enduring symbols of industry. Cutting its 2005 earnings outlook by more than half, the No. 1 automaker expects to lose $1.50 a share in the first quarter and earn just $1 to $2 a share for all of 2005. The company had previously predicted a break-even first quarter and earnings of $4 to $5 a share for 2005. The warning led Fitch to cut its rating of GM and GMAC's corporate debt to triple-B-negative, its lowest investment grade level. "Even though they had planned for some weakness early in the year, their business has been significantly weaker than expected," said Morningstar analyst Phil Guziec. "They've got huge operating leverage, so that crushes earnings." GM's stock closed down $4.71, or 14%, to $29.01, falling through its 52-week low of $33.69 and setting a 13-year closing low. The Dow Jones Industrial Average, meanwhile, lost 113 points Wednesday. GM has been a virtual spigot of bad news so far this year. Sales faltered in February, as the company announced it was cutting back on production. That followed a previous slash in earnings guidance for the year. Now, with the broader economic recovery gaining strength and foreign auto manufacturers rapidly stealing market share, an even deeper cut in guidance has prompted analysts to ponder significant changes in strategy at GM that could jeopardize its leadership position in the worldwide auto market. Having once laid claim to more than 50% of the U.S. market, GM now has just about half that, and its shares are still in decline. A boom in demand for sport utility vehicles and trucks in the 1990s silenced widespread predictions from the previous decade that Japanese automakers, like Toyota ( TM) and Nissan ( NSANY), would overtake their American counterparts. But with oil prices topping $55 a barrel and lighter vehicles coming back into fashion, the specter of a change in leadership has been raised again.