NEW YORK (CNN/Money) - Detroit will soon start to grapple with the problem of how to sell a better mileage, lower emission vehicle to buyers who in the past generally haven't cared about fuel mileage or the environment -- sport/utility vehicle and pickup truck owners.

Convincing American consumers that green doesn't equal weak will be a challenge. It will be crucial, though, since fuel economy and cleaner air alone do little to sell vehicles on a mass-market basis. Relatively gas-guzzling light trucks, including pickups and SUVs, are huge sellers in the United States.

On a strictly rational basis, improved fuel economy alone probably won't justify the $2,500 to$3,000 added to the sticker price for the hybrid version, even if gas prices go up and stay up.

Hybrid GMC Sierra

U.S. automakers need to sell these vehicles in order to raise their average fuel economy as a way to meet U.S. regulations and California environmental regulations, and as part of a broader long-term research and development effort to find a replacement for the internal combustion engine. So far only two Japanese automakers -- Toyota Motor Corp. and Honda Motor Co., have hybrid vehicles for sale in the United States, but the Big Three are all close to debuting their hybrid offerings.

So, when General Motors Corp. (GM: down $0.07 to $43.90, Research, Estimates), Ford Motor Co. (F: up $0.23 to $12.18, Research, Estimates), and DaimlerChrysler's (DAX: Research, Estimates) Chrysler Group start rolling out SUVs and pickups with hybrid engines during the next year, they will be stressing that the vehicles are more than just green machines. Instead they will point to the power of the vehicles, both on the road and in their ability to run electrical machines loved by American buyers.

The hybrid engine couples a traditional gas or diesel engine with an electric motor. The electric motor takes over some of the work of the gas engine, especially when the vehicle is idling or traveling at low speeds. In turn, some of the power from the gasoline engine charges the batteries for the electric motor.

That power-sharing arrangement allows the gas engine to operate much more efficiently, which saves fuel. But more efficiency also means more power, so that a four-cylinder engine can give you the punch of a six. (This set-up also means that city driving mileage is sometimes better than highway mileage, the opposite of the typical gas-only engine.)

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The first hybrid vehicles to come out of one of the Big Three will be General Motors pickup trucks -- Chevrolet Silverados and GMC Sierras -- which are slated to be available for fleet sales to businesses, such as contractors, later this year. Regular consumers will be able to buy these trucks in mid-2004.

These hybrid trucks will each sport two 110-volt electrical outlets.

"That lends itself to commercial use," GM spokesman Matt Kester said. "You can turn it on, lock the doors, and use it as a stationary generator."

The GM pickup hybrids are going to see only about a 10 percent gain in fuel economy -- to about 20 miles per gallon from 18 for a comparable gasoline version of the trucks. So the savings that will attract buyers are more likely to come from not having to haul around a generator to power saws, drills and air compressors.

Next up from the Big Three will be Ford's Escape SUV, due late summer of next year. The hybrid Escape is expected to show a modest 16 percent improvement in highway mileage over a regular, gasoline-powered, Escape. But it will get nearly double the city gas mileage. But that's not necessarily going to be the focus of the SUV's marketing campaign.

"It all depends on what customer is looking for," Ford spokeswoman Susan Krussel said. "Certainly the Escape hybrid provides fuel economy, but different customers take different criteria into consideration. We'll be selling this as a 'no compromise' SUV. It's going to have all of the power and performance of base Escape."

Chrysler's first hybrid will be a Dodge Quad Cab pickup that will combine a diesel and hybrid engine, due out next fall. Chrysler spokesman Max Gates sales fuel economy won't be the main driver of sales, even though the diesel-electric engine will have 30 to 40 percent better mileage than a typical gas version, although only 10 percent better than a comparable diesel-only model.

"I think we think of it more as a performance vehicle," he said. "The hybrids that are out there right now are economy cars. This isn't that. The outlets in the box replace dragging around a portable generator behind you. This gives something value added to customer that offsets the higher cost of the hybrid power train."