-- General Motors Corp. offered detailed plans today to boost the fuel economy of its most popular cars and trucks by as much as 50 percent, beginning with two pickup trucks in the 2003-model year.

Overall gains in fuel economy will range from 15 percent to 50 percent, with the biggest increases going to the 2005 version of the compact Saturn VUE sport utility vehicle, GM officials said.

As In Overdrive first reported last month, GM will rely on hybrid gas-electric technology, and possibly hybrid diesel-electric engines, to dramatically crank more miles per gallon out of its mid-size sedans, such as the Chevrolet Malibu, and its full-size SUVs, such as the GMC Yukon.

GM is the world's largest car company. If it is successful in winning widespread consumer acceptance of hybrid petroleum-electric vehicles, it could change radically the kinds of engines and propulsion systems that could go into future cars and trucks.

Clearly, that is why GM is using the North American International Auto Show, which opens here to the global media Sunday, to make its announcement. The company, long maligned as a laggard in the development of fuel-saving technology, is throwing down the gauntlet.

"Although today's hybrid market represents relatively low volumes [of sales], we are well-positioned ton meet any market demand that may develop," said GM President and Chief Executive Officer G. Richard Wagoner.

"In fact," Wagoner said, "if consumers were to select the hybrid option on all of the models included in our multi-year plan, it could eventually exceed [sales of] one million vehicles [annually]."

Currently, Toyota Motor Corp. and Honda Motor Co. Ltd. are the leaders in the development and sales of hybrid gas-electric models. Toyota markets the Prius. Honda sells the hybrid Insight two-seater and its new-for-2003 gas-electric Hybrid Civic sedan. But current combined sales of those small cars barely total 15,000 a year.

After much internal debate, GM's top leaders decided to pursue a mass-market hybrid vehicle strategy.

"We didn't know if this was the right thing to do," one GM executive said. "We're talking hundreds of millions of dollars here. Billions, probably. We had to ask ourselves if it made more sense to put all of that money into fuel cells, which is where we want to go, or to risk it on hybrids."

The company's executives decided "to go big" with hybrids as an interim strategy largely because the world was beginning to regard Toyota and Honda as the true leaders in fuel economy, another GM executive said.

"We have to have credibility as innovators in fuel economy if we want consumers to accept what we plan to offer in fuel cells," the executive said.

Hydrogen fuel cells generally are viewed by auto manufacturers and environmentalists as the key to fuel conservation and the elimination of tailpipe pollution in automotive transportation. Fuel cells produce electricity to drive wheels through an electrochemical reaction between hydrogen and oxygen. Water vapor is the primary byproduct.

All major car companies have fuel cell development programs. But, despite much progress and the announcement of some upcoming fuel cell demonstration projects, most industry analysts and experts estimate that it will take another decade for fuel cells to become commercially viable.

That's a long time to be working on the next big thing while rivals such as Toyota and Honda are getting kudos for pushing gas-electric, fuel-efficient hybrid engines.

Wagoner and his lieutenants decided not to wait.

GM will offer three types of optional gas-electric hybrid systems, which will add around $2,000 or $3,000 to the cost of vehicles in which they are installed. Wagoner said that he hopes federal and state governments will help to offset that cost through tax credits to consumers who buy the hybrids.

The most sophisticated system, employing dual electric motors and an array of sensors to help those motors work in tandem with the gasoline engine, will go into the 2005 Saturn VUE sport-utility vehicle. GM executives said that new propulsion system will give the VUE a 50 percent boost in fuel economy, raising it to nearly 40 mpg.

Compact/midsize cars such as the new Chevrolet Equinox and the completely restyled 2004 Malibu will get an "electric assist" hybrid setup, similar to the one currently used in the Honda Civic Hybrid. Under that system, the electric motor helps to reduce fuel consumption and tailpipe pollution by taking over for the engine in low-efficiency driving, such as urban stop-and-go driving where much fuel is wasted in idling. The company expects a 15 percent improvement in fuel economy with those models.

GM's pickup trucks will get a version of "electric assist" with a twist. For example, some versions of the 2003 GMC Sierra and Chevrolet Silverado full-size pickups will be equipped with the company's Displacement on Demand engines.

Depending on driving demands -- high speed and heavy cargo load, low speed and light cargo load, for example -- the DOD engine will use half, or all of its cylinders. In low speed situations, for example, half of an eight-cylinder engine bank could be working with the assistance of an electric motor. With four cylinders resting when they aren't really needed, the DOD system cuts fuel consumption and pollution. GM's executives believe the system could improve pickup truck fuel economy by as much as 20 percent.

GM hopes to have all of its gas-electric and diesel-electric models in place by 2007. In the interim, Wagoner said, the company will continue working on fuel cells and improving traditional internal combustion engines.

"There is no one answer," Wagoner told Overdrive in a recent interview. "There are going to be several different systems existing at once. We've got to go to market with all of them."