Washington Bureau - JIM TANKERSLEY Reporting from Dearborn, MI

In an upstairs test lab at the world headquarters of Ford Motor Company, engineers in white coats are revving up a turbocharged engine that screams with the muscle car power that once made Detroit the envy of the world. On a curb outside sits a prototype electric vehicle with all the chest-thumping character of a canoe.

Surprisingly, while fuel-sipping, climate-friendly hybrids and electric cars like that prototype command the spotlight these days, both Detroit and the Obama administration are betting their survival on that monster up in the lab. Over the next decade at least, some experts say Detroit's viability--and the success of the Obama administration's early moves to combat global warming – will hinge less on super-efficient hybrids or electric bubble cars than on improving the fuel-efficiency of the larger vehicles in Detroit's fleet without sacrificing performance.

In short-hand terms, that means the "Holy Grail" for domestic automakers is designing the equivalent of a full-sized pick-up truck that gets 18 miles per gallon, up from 15, and still has the power to haul a boat or tote a load of 2x10s.

For decades, the world's best-selling vehicle of any kind has been the Ford F-150 pick-up. Now, as gas prices spike and Americans reshape their car buying habits, Ford and makers of its equally brawny rivals must respond to more mileage-conscious buyers. But it's not just about pickup trucks. The kind of incremental improvements Ford and other domestic automakers are seeking for their largest vehicles reflect a strategy that also extends to their full-sized and intermediate cars as well.

Chrysler has rolled out a set of emission-reducing four cylinder engines and is developing a high-performance, higher-efficiency line of six cylinders called the "Phoenix Engine." General Motors is betting big on the plug-in Chevy Volt – but also heavily touting the class-leading 21 mpg of its Silverado XFE pick-up truck.

Some researchers expect these moves to yield big financial rewards: Boosting the fuel economy of their fleets to meet the new federal greenhouse gas emissions standards would gross the Big Three $3 billion a year in new profits, a study from the University of Michigan's Transportation Research Institute reported this summer.

Industry executives say simply going "greener" won't be enough to beat foreign competitors. While improving fuel economy, American manufacturers will need to attract buyers for the same reason they always have: Their size and carrying capacity fit many consumers' needs better than mini-cars do.

The Obama administration seems to agree. Ford recently got a $6 billion Energy Department loan in part to develop what it calls the EcoBoost engine, which must deliver the power of today's engines with up to 20% better mileage. By 2013, 90% of Ford vehicles will carry the EcoBoost - including the F-series trucks. Ford executives say that's the only way to bridge the gap between yesterday's gas-guzzlers and the plug-ins and hybrids they believe will dominate a more distant future.

"We're going to try to wring as much efficiency as we can out of this technology until the other technologies are on line," said Dan Kapp, Ford's director of research and advanced engineering.

America's love affair with unbridled horsepower peaked in 2004, the last year in which U.S. gas prices averaged less than $2 a gallon. As prices rose, the SUVs and pick-up trucks that once made up nearly 60 percent of U.S. auto sales steadily lost market share to smaller, more efficient cars. The average fuel economy of the U.S. new car fleet improved accordingly.

Even with that shift, however, sales figures show that nearly half the passenger vehicles sold in the United States this year have been light trucks – a category that includes medium and large-sized SUVs.

The enduring popularity of those larger vehicles owes something to image, marketing experts say.

But a large part appears to be practicality. Contractors lug construction equipment between job sites. Electricians and plumbers must haul tools and replacement parts. Florists, dry cleaners and other service providers need big panel trucks.

"We have customers whose livelihoods depend on the F-Series," says Derrick Kuzak, Ford's group vice president for product development, "But we're going to produce an F-Series that is much more fuel efficient."

As for non-commercial buyers, many families want carrying capacity not just for their kids and pets but for car-pooling, ballet and the soccer team – not to mention towing jet-skis to the lake or hauling new washers and dryers home from Lowe's or Home Depot.

"We the public have always wanted low gas prices and large cars, and that's what Detroit always produced," says Kent Hughes, an auto-industry analyst who directs the Program on America and the Global Economy at the Woodrow Wilson International Center for Scholars in Washington.

The increasing importance consumers attach to fuel efficiency gives the Obama administration an opening for its attempts to save Detroit while cutting the greenhouse gas emissions that scientists say cause global warming.

As part of a multi-front push, the Energy Department set out this year to make billions of dollars in loans to reduce emissions by improving vehicle efficiency. The first round of loans included $2 billion for electric vehicles, awarded to Nissan and Tesla, which promised big improvements for a small number of buyers. But Ford got $6 billion because its promised gains, while smaller, would involve a much larger number of vehicles.

The result is a series of engines that deliver the torque and horsepower of larger traditional engines. Ford engineers say a 3.5 liter V-6 EcoBoost, for example, outperforms the standard V-8 often favored by pick-up owners.

The EcoBoost builds on the ideas behind high-performance diesel engines that Ford deployed in Europe several years ago. In the Dearborn lab, engineers combined turbo-charging – a process of compressing air flow into an engine – with specialized direct fuel injection, in order to yield the more power for less gasoline.

The engine adds $3,000 to an average vehicle. But simply improving the fuel economy of a standard F-150 pick-up by 20 percent, from 15 to 18 mpg, saves roughly a gallon of gas for every 100 miles driven. That's the same gallons-per-miles savings you'd get by boosting a small car's economy from 33 to 50 mpg.

All told, the Energy Department estimates, fleet-wide improvements funded by the government loans will save U.S. drivers 200 million gallons of gas a year on Fords alone.

And its domestic competitors, who are pursuing a similar strategy, are expected to produce still more savings.