THE RACE TO BUILD A SUPERCAR THE BIG THREE AUTOMAKERS ARE TEAMING UP TO BREAK THE MILEAGE BARRIER.(MAIN)

Byline: GLENNDA CHUI - Knight-Ridder

The Big Three automakers and the federal government signed on this fall to develop safe, clean cars that travel 80 miles on a gallon of fuel. They spoke of breakthroughs so revolutionary that they might be impossible to achieve.

But some experts believe mileage could be dramatically improved using technologies available today -- that the average car could now get 40 or even 45 miles per gallon, rather than the current average of about 28.

So why aren't we making them?

The obstacles are more political, social and economic than technical, observers say -- and they'll probably be tougher to overcome.

Some versions of the car of the future are already venturing onto the road.

More than 50 solar-powered cars have been racing across Australia this month. Electric car technologies are advancing rapidly, spurred by California's requirement that car companies start selling models that give off no pollution by 1998.

Engineers have also found ways to make ordinary gas-powered cars far more efficient.

Some features, such as front-wheel drive and fuel injection, are already widely used. Indeed, the average mileage of new cars has increased 76 percent since 1975 to 27.8 miles per gallon -- just above the standard required by federal law.

But other improvements, such as the lean-burn engine and tires that roll more easily, have barely dented the market. …