How does a midsize sedan with a V6 engine sound? Not very exciting, right? Well, how about if it got 80 miles per gallon? Ah, that's a different story, isn't it.

It wasn't on the same level as the discovery of DNA or the invention of the superconductor, but the lightweight steel auto body rolled out Wednesday in Detroit may end up being the best thing to hit the automobile industry since the automatic transmission."Today we have demonstrated with our UltraLight auto body that steel has enormous potential to reduce weight while improving structural performance and crashworthiness, and costing less than today's car bodies," said Robert J. Darnall, chairman of the American Iron and Steel Institute, at the unveiling.

The UltraLight Steel Auto Body Project, begun in 1994, has produced an affordable steel body for a midsize car that would weigh about 2,960 pounds, without secondary weight savings, compared with an average 3,300 pounds for today's midsize cars.

But Darnall challenged the Partnership for a New Generation of Vehicles, a $22 million joint venture of the federal government and the auto industry, to design and produce a steel-bodied, affordable midsize car weighing a super svelte 2,000 pounds - about the same as a 1974 Volkswagen Beetle.

"We have shown that lightweight and steel is not an oxymoron," said Darnall. "Now we want to take weight reduction to the next level and test the true potential of steel."

Darnall conceded that building a modern midsize car that weighs only a ton would be a "huge undertaking" but promised that the steel industry is up to the challenge if the auto industry has equal foresight.

If it does, it would mean a major leap forward in performance and fuel savings. For decades, vehicle designers have worked at finding ways to reduce weight without comprising safety. Aluminum is an obvious solution, but its so expensive that it has been used in quantity only in mega-upscale cars such as the Audi A8.

Darnall, who is also president and CEO of Inland Steel, said the UltraLight project proves that a steel body in a family sedan can meet or exceed a wide variety of performance and cost targets while maintaining high safety standards.

If adopted by one or all of the Big Three U.S. automakers, it is expected that the 1-ton car envisioned for the new UltraLight body would triple the fuel efficiency of current midsize sedans to about 80 miles per gallon.

But it would do even better, Darnall noted, in a body structure optimized for low or zero-emission powerplants such as diesel-electric hybrids or fuel-cell electrics that are said to be on the "near horizon" of General Motors and others.

The lightweight auto body unveiled Wednesday does not have a motor, but the design assumed the use of a V6 engine typical of today's family sedans.

With Wednesday's unveiling of the UltraLight steel chassis, the ball - or body - is now in the automakers' court.