In a sign of how major automakers are spreading their bets because of an uncertain environmental future, General Motors has acquired an undisclosed stake in a startup firm funded by venture capitalist Vinod Khosla that says it can produce ethanol from wood chips, storm debris, and municipal waste, and do it more economically than companies that use corn or sugar.

G.M. announced its investment in two-year-old Coskata Inc. of Warrenville, Illinois, on Sunday, the opening day of the North American International Auto Show in Detroit, a time and venue usually reserved for new vehicles or important corporate news.

The investment illustrates how G.M. in particular is dabbling in almost every green technology on the market, including hybrid gas-electric vehicles, all-electric autos, flex-fuel cars and trucks, and even a Korean-made gasoline-powered compact that squeezes 37 miles from each gallon in city driving.

Until relatively recently, G.M. focused much of its efforts -- both in public relations and engineering -- on hydrogen fuel cells. In 2003, at another Detroit auto show, G.M. was touting its Autonomy fuel-cell "skateboard" project as the future of transportation.

But hydrogen fuel cells remain a long-term bet compared with cars such as the Toyota's hybrid gas-electric Prius, which is already on the road, and selling in the hundreds of thousands around the world. G.M. is putting about 100 hydrogen fuel cell vehicles on the road this year through a program it calls Project Driveway.

This latest effort is part of G.M.'s support for alternative fuels -- most notably vehicles that can run on E85, a mixture of 85 percent ethanol and 15 percent gasoline -- that can be used in existing "flex-fuel" vehicles that G.M. already produces by the hundreds of thousands.

Coskata claims it can turn everything from wood chips, storm debris, and municipal waste into ethanol using a bacterial process that is more energy efficient and less controversial than traditional ethanol processes made from food sources, such as corn and sugar. Recently, ethanol from food supplies has come under attack because ethanol producers' demand for corn has increased the price to consumers.

But Coskata is still years away from producing ethanol in large quantities. It has yet to build a planned 40,000-gallon pilot plant. Nor has it announced specific plans for a major production facility, which its executives say can take two to three years to build and an investment of $300 million to $400 million.  Company executives did say they planned to enlist partners to build the plants, not build them on their own.