(FORTUNE Magazine) – If you're willing to set aside the gigantic chicken-and-egg problem of where to get the hydrogen for a new generation of hydrogen-powered cars, then GM has a hell of a story to tell. The automaker has just revealed the depth and breadth of its cloistered program to develop vehicles powered by fuel cells, which produce electricity by combining hydrogen gas and oxygen. The only byproduct: water vapor. "Fuel cells are very important to GM's future," says CEO Rick Wagoner. "We've spent hundreds of millions already, and we're going to spend a lot more than that until we get into production vehicles."

Just as important, the fuel-cell program has inspired a radical rethinking of auto design. GM is now out on the auto-show circuit displaying its new "skateboard" chassis (pictured above): a flat, six-inch-thick platform that will hold the hydrogen fuel, a raft of power electronics, and all of the other parts that make the car go. It won't need a transmission or drive shafts; wires will deliver power directly to four lightweight electric motors integrated into the wheels. Customers will choose from among several interchangeable body styles, and GM will simply fasten the top to the chassis. Software will match the feel and handling of the vehicle to its style.

Skeptics may note that GM has had grand plans before; the Saturn and electric cars were also supposed to revolutionize auto design. Most carmakers are working on fuel-cell systems too, and both Toyota and Honda will field small numbers of test vehicles next year. GM doesn't expect to roll out fuel-cell cars commercially before the end of the decade. But being first to market is not GM's goal. "We want to be the first to sell a million of them," says GM research and development VP Larry Burns. For a clean, green car program, that sounds almost businesslike.

--Stuart F. Brown