Auto shows have long been the industry’s fantasylands, places where automotive dreams come true. In other words, they’ve been geared to lavish displays of superpowered rides and futuristic concepts.

Yet while 600-horsepower sports cars like the 2009 Corvette ZR1 are still making their debuts at the North American International Auto Show in Detroit, more automakers are unveiling not the raciest, most powerful designs they can come up with, but fuel-sipping rides and alternative-fuel technologies. At this year’s show, which opens with media previews today, there is an unprecedented range of earth-friendly models. And that extends even to the luxury automakers, who have long pursued acceleration rather than conservation, but are showing off ethanol-eating S.U.V.’s, plush hybrid sedans, and more efficient diesel-powered sports coupes.  

Squeezing more miles from a gallon of gas is an especially delicate balancing act for makers of luxury cars, whose customers demand spacious, hefty vehicles with major muscle and all the latest gadgets. But automakers have seen the writing on the wall—or more accurately, on the mileage stickers affixed to every new car and truck: The 2007 energy bill signed into law in December calls for a nearly 40 percent jump in fuel economy standards over the next several years, the first major adjustment in decades, and eliminates mileage breaks for heavier S.U.V.’s, pickups, and minivans. (See slide show.)

“We can provide our models from Europe that tend to be smaller and have higher fuel economy,” said Thomas Plucinsky, BMW’s spokesman. “But U.S. customers still want larger vehicles, so the trick is to give them the size and performance they demand while still boosting efficiency.”

As a result, we have Detroit unveilings such as the Cadillac Escalade Hybrid, a gas-electric version of this three-ton monument to S.U.V. excess. On sale this summer, the electric-boosted Escalade is designed to deliver roughly 20 miles per gallon in the city, a significant gain over the 12 to 13 m.p.g. of the gas-only model.

G.M. developed its hybrid system with BMW and the former DaimlerChrysler, and both BMW and Daimler-owned Mercedes are showcasing their versions in Detroit. BMW’s X6 ActiveHybrid concept is a preview of a production crossover S.U.V. hybrid that will reach showrooms in 2009. (BMW claims a 20 to 25 percent overall gain in fuel economy.) Mercedes’ ML450 will incorporate the hybrid system when the midsize S.U.V. goes on sale the same year, along with a V-6 hybrid version of Mercedes’ flagship S-Class sedan.

David Cole, director of the Center for Automotive Research in Ann Arbor, Michigan, said that luxury buyers may be an easier sell for fuel-saving technologies—including hybrids and diesels—that still add thousands of dollars to the cost of a car. “Wealthier buyers can better afford to be green, and they probably pay more attention to how they appear in the eyes of the world,” Cole said. Diesels currently add roughly $1,000 to $5,000 to a model’s cost, while hybrid technology adds anywhere from $3,000 to $30,000, the latter for the Lexus LS 600h L sedan.

Saab, G.M.’s Swedish luxury division, unveiled the 9-4X BioPower, a crossover S.U.V. concept model that’s ethanol compatible. Meanwhile, G.M. Chairman Rick Wagoner used the Detroit show Sunday to announce a breakthrough in producing cellulosic ethanol from waste products, which promises economic and environmental advantages over ethanol made from corn and other food crops. Wagoner announced a partnership and equity stake in Coskata, an Illinois company that claims it can get production costs for cellulosic ethanol to under $1 a gallon—cheap enough to make it competitive with gasoline.

As some automakers prepare to blitz America with the fuel-efficient, clean-diesel cars that dominate the European market, BMW showed the 335d sport sedan and the X5 xDrive 35d sport-utility—diesel-driven versions of familiar, popular BMWs sold in the U.S. Both will reach U.S. dealers this fall, and will utilize urea-injection technology—which uses an ammonialike fluid that neutralizes tailpipe pollution—to meet stringent new federal emissions requirements that are coming in 2009.

The most show-stopping diesel is a concept version of the Audi R8 sports car, the Porsche 911 competitor that has won a slew of international automotive awards. The diesel version, though not yet green-lighted for production, features a 500-horsepower, turbocharged 12-cylinder engine that could easily top 20 m.p.g., versus about 15 m.p.g. for the gasoline version. It draws on the diesel technology Audi used to dominate recent runnings of the 24 Hours of LeMans with its groundbreaking R8 racers.

The drive for economy is being spurred by more than the energy bill provision. California and more than a dozen other states are demanding the power to regulate greenhouse gas emissions linked to global warming, and have sued the Environmental Protection Agency for the right to set their own carbon dioxide standards. Since carbon dioxide emissions are almost entirely a function of fuel economy—meaning a car that gets 40 m.p.g. produces about half the greenhouse emissions of one that gets 20 m.p.g.—any new mandates would effectively force automakers to achieve even more dramatic mileage gains.

Luxury automakers face the same pressures in Europe, where environmental critics are calling for sharp cuts in greenhouse gas emissions. The European Parliament has called for reductions that would effectively require gasoline cars to get 43 m.p.g., and diesels 48 m.p.g., by 2012.

For more than 20 years, some luxury automakers here have chosen to pay fines rather than bring their cars into compliance with U.S. mileage standards. For 2007, DaimlerChrysler’s Mercedes division was fined a record $30 million for its cars that fell short on fuel economy.

Since automakers’ entire fleets must meet fuel economy averages, many avoid fines on luxury and sports cars by offsetting their low mileage with sales of thrifty compacts. Yet the wave of green-minded luxury cars shows automakers preparing for a new reality: one in which even the highest and mightiest machines are no longer immune to environmental demands.