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Automakers are using more aluminum as a weight-saving alternative to steel, sparking debate over which metal is best.

The aluminum industry says its metal is light, strong and less corrosive than steel.

The steel industry says its metal is cheap, more flexible and easier to process.

Aluminum is the fastest-growing major component in new cars and trucks. In 1999, the average vehicle contained 236 pounds of aluminum, up from 112 pounds in 1978, according to American Metal Market, an industry newspaper.

During the same period, regular sheet steel declined to 1,399 pounds from 1,915 pounds.

"Aluminum is replacing steel in certain models where automakers want to meet weight and fuel economy targets," says Al Wrigley, an editor at American Metal Market. "But aluminum has to get its cost down to really compete against steel."

Steel typically costs between 20 cents and 30 cents a pound while aluminum sells for more than $1 a pound. Aluminum companies argue that one pound of aluminum replaces two pounds of steel, and wide use of lighter-weight aluminum allows automakers to use other lighter, cheaper parts, such as brakes and tires, which further cuts costs.

Using aluminum components, in fact, can reduce the weight of parts by up to 50%. "We use aluminum because it is a lightweight material that improves the overall efficiency of the vehicle," says Jeff Kuhlman, a General Motors spokesman.

Some parts, such as aluminum alloy wheels, have been around for years. More recently, components such as engine blocks, hoods, body panels, frames and suspension parts are made of aluminum.

Some vehicles with aluminum parts:

* The Audi A8 uses an aluminum frame, body panels and other components.

* The 2000 Lincoln LS sedan has an aluminum hood, trunk lid, suspension parts and V-8 engine.

* GM's redesigned Suburban, Tahoe and Yukon sport-utility vehicles have aluminum liftgates.

To counter aluminum's growing influence, steel companies have banded together to create ultralight steel, sometimes called high- strength steel. It's 34% lighter than conventional steel but stronger. It's also more expensive than regular steel but still cheaper than aluminum.

Use of high-strength steel has grown to 328 pounds in the average vehicle in 1999 from 112 pounds in 1978. And the steel industry brags that Ford Motor replaced the aluminum trunk lid of the Taurus with a steel lid for the 2000 model.

Because of design problems, Jaguar uses a steel hood on its S- Type instead of an aluminum hood like its platform cousin the Lincoln LS.

The new Saturn L-Series midsize sedan has a roof, hood and fenders made of steel instead of plastic body components found on the smaller Saturn S-Series.

Darryl Martin, a spokesman for the American Iron and Steel Institute, says most vehicles today have between 20% and 40% high- strength steel. But he predicts use of it will grow.

Even so, automakers are banking a good part of the future on aluminum.

In March, GM signed a 13-year, $1 billion deal to buy recycled aluminum from IMCO Recycling.

GM showed a concept car at the Detroit auto show that has aluminum body parts and other components and gets 80 miles to the gallon. Ford showed a concept car called Prodigy in Detroit that also uses aluminum parts and gets more than 70 mpg.