Not long after Dan Kroushl got his new 2004 Toyota Prius, he began to wonder about the mysterious button on the dash. It didn't seem to have any function. Didn't boost the turbo or engage an ejector seat. In online discussions with other Prius enthusiasts, Mr. Kroushl soon discovered the button did have a hidden function: It could turn the gasoline-electric hybrid into an all-electric car - for a mile or so on limited battery power.

This "stealth mode" button works fine in Japan and Europe where it's handy for drivers to roll politely about densely packed subdivisions in the early morning and late evening. But the button has been disconnected for North America's Priuses.

Now, scores of Prius owners in the United States are activating the button on their own - despite company warnings that altering the car will void its warranty.

Some drivers, including Kroushl, are going even further: adding battery capacity - and a plug. The hoped for result: a high-tech commuting car that plugs into a socket at night and gets amazing gas mileage the next day.

In effect, these backyard mechanics have turned the hybrid car's appeal on its head. Instead of emphasizing gasoline over electric power and the convenience of today's cars, they're aiming to create less polluting higher-mileage vehicles that emphasize electricity over gasoline - even if it's a bit less convenient.

"One guy I know plugs his Honda hybrid into a windmill for power," Kroushl says. "It costs him practically nothing to drive."

Since before the Model T, electric cars have been among the most efficient modes of transportation. They made a bit of a comeback in the mid-1990s, when General Motors and other automakers reintroduced electric-only cars to meet a proposed California clean-air mandate. But with the weakening of that requirement, which called for some vehicles to be zero-emission in 2003, GM, Toyota, and Honda stopped production of their electric vehicles. Some automakers, which had leased the cars, began taking them back to be destroyed.

Only the dedication of enthusiasts has kept them from disappearing completely. This past summer, after Ford Motor Co. announced it would scrap its electric Think vehicles, environmental groups occupied the roof of the company's Norwegian offices and held a mock funeral at a San Francisco dealer. Within two weeks, Ford agreed instead to ship its vehicles to a Norwegian electric-car manufacturer. Just last week, Ford also reluctantly agreed to let Dave Bernikoff-Raboy, a California rancher, buy the all-electric pickup truck he had been leasing. He was so devoted to the vehicle, which recharged off a solar panel, that he camped out near a Ford dealership in Sacramento, Calif., to protest that automaker's plans to dispose of its remaining electric fleet.

Now, a growing interest in hybrids has rekindled the hopes of the electricity-firsters. Global demand for hybrids is estimated to rise from about 200,000 units produced annually to more than 1 million vehicles a year by 2010, according to ABI Research, an international market-research firm, in a report last year. If only 1 percent of these were converted to run primarily on electricity, it would create a base of more than 30,000 vehicles by the end of the decade.

"We're not talking about electric vehicles, but about plug-in hybrid vehicles that can be topped off with electricity for short trips," James Woolsey, former director of the Central Intelligence Agency, said last month during the unveiling of a report by the 16-member National Commission on Energy Policy. "The potential in terms of national policy, and in terms of global warming, ought to be focused on by anyone" concerned about terrorism or "paying over $2 a gallon."

Other experts are also urging automakers to take a new look.

"We think the transportation fuel sector should be diversified by utilizing more electricity as a fuel - plug-in hybrids that can get 100 miles per gallon and allow you to run on electricity alone for 20 to 30 miles, then shift to the combustion engine," says Gal Luft, director of the Institute for the Analysis of Global Security, an energy-security think tank in Washington.

But automakers show little interest.

"Why would anyone want to do that?" wonders Sam Butto, a Toyota spokesman in Torrance, Calif., when told some Prius owners are creating their own plug-in Priuses. "One of the great features of the Prius is that you don't have to plug it in."

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