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.

In addition to its financial investment, G.M. plans to use fuel produced by Coskata's pilot plant at its Milford Proving Grounds facility to test how well it performs in vehicles. The two firms say the pilot plant, likely to be built in the Midwest, will be operational by the end of 2008.

"This is a pretty big move for us," said Mary Beth Stanek, G.M.'s director of environmental and energy policy and commercialization. "It's a tighter relationship so that we can commercialize the idea more quickly."

She spoke along with Coskata's president and C.E.O. William Roe during an Internet web conference to brief journalists prior to Sunday's announcement. Journalists attending were required to agree to an embargo on the information for noon today -- heightening the sense that the announcement was important.

G.M.'s vision of itself as a leader in the environment has evolved dramatically during the past decade. In the mid-1990s, it continued to build larger, less fuel-efficient vehicles with higher profit margins even as its competitors' put them on their drawing boards.

Stanek calls recent moves a crystallization of the projects that G.M. has invested in over the years, not necessarily a shift in strategy. "We are still as hot on hydrogen as we have been," she said. "But now we are moving hybrids, plug-in electrics, and fuel cells out of research and development, and commercializing them."

Today, G.M. is dabbling in almost every green technology on the market. But a main stalling point for many of the ventures -- and one that may include Coskata -- is that turning great technological ideas into real cars or economically viable fuel alternatives has proven to be tough and time-consuming.

The company has been touting its Chevy volt all-electric vehicle for more than a year, but still hasn't worked out the bugs in the battery technology. The Autonomy fuel-cell project has been around for years and is just now showing evidence of moving beyond the lab. Even E85 has had problems in terms of creating the infrastructure to deliver the fuel to consumers with flex-fuel vehicles.

But G.M. can't stop making bets, given the pressures it faces from competitors, government, and even consumers.

Toyota, now a serious contender for G.M.'s long-standing rank as No. 1 car company in the world, assumed the mantle of environmentalism much earlier than G.M. in part because of the success of the Prius.

Consumers also are now searching for cars that are more fuel-efficient as crude oil tops $100 a barrel and retail gasoline prices seem stuck above $3 a gallon around the country.

G.M. has been solidly behind ethanol, primarily produced from corn, for years. In early 2006, it launched a marketing campaign called "Live Green, Go Yellow" to make consumers aware of its flex-fuel vehicles and E85. The "yellow" in the tagline referred to corn.

Coskata maintains that it can produce ethanol from old tires, municipal waste, even debris from hurricanes through its bacterial process for about 50 cents to a $1 a gallon. William Roe, the company's president and C.E.O., says gasoline costs between $1.90 and $2 to produce.

Ethanol from corn also has other downsides. It takes almost as much energy to produce as it saves when used. Coskata claims that its process makes ethanol that produces up to 7.7 times more energy than is consumed in production.

Those numbers were arrived at by a study that Coskata commissioned from the Argonne National Laboratory. The figures are based on the company's existing research and development, not on real-world manufacturing plants.

Coskata's process is part science fiction and part simple chemistry. "Feedstock," or the primary ingredient used to create the fuel is put through a feedhandler. That feedstock can be any carbon-based material. But Roe did say that "bone dry, free and easy to handle" feedstock works the best.

While Roe played up the idea that municipal solid waste could be used, he noted that it is trickier to use. "It can be wet and there are other challenges since the waste coming in differs day to day," he said.

The feedstock is then delivered into a gasifier that breaks down whatever is fed into it into "syngas," a mixture of hydrogen, carbon monoxide, and carbon dioxide. It is then passed through a scrubber to remove particulates. The gas is cooled and sent to a "biofermentation" system that uses plastic tubing instead of the tanks most traditionally used in ethanol production.

This is where science fiction kicks in. Using proprietary bacteria acquired from the University of Oklahoma, the cooled "syngas" is consumed by bacteria in the tubing. The bacteria's digestive process has been manipulated to create only ethanol and water.

Roe claims that Coskata's system can produce 100 gallons of ethanol from a dry ton of carbon-based "feedstock." The ethanol-water mixture is then passed through a membrane that separates the two. The recovered water is then re-used in the bioreactor, leaving only ethanol, the company said.