High-mileage cars of future take shape now

It looks like a cross between a missile and a motorcycle, complete with outrigger wheels and twin headlights. The vehicle, dubbed ''Litestar,'' is long and low to the ground, with a hatch top that slides back to let driver and passenger slip into tandem seats. Best of all, its designers say this ''car of the future'' gets more than 100 miles per gallon on the highway.

If all goes according to plan, the first production models of these two-seaters will slide off the assembly line next month.

''The auto industry has left a niche for someone like us'' in the small-car category, says Stan Leitner, president of the St. Louis-based Tomorrow Corporation, which is producing the vehicle.

The project illustrates the continuing quest - even in the face of slumping fuel prices - to build ''ultra-high-mileage cars.'' Auto designers have long sought ways to boost fuel efficiency, shaving off useless tailfins and switching to lighter materials. This helped push top mileage into the 50 m.p.g. range.

But design experts say progress toward even better mileage in the future will demand leaps of innovation, changing the way cars look and operate.

The buzzword in high-mileage design is aerodynamics - shaping exterior surfaces that cut drag and let cars slip through the air with the least possible resistance.

Taking this into account, the front ends of cars, for instance, are likely to become narrower and lower to the ground. The trend is already clearly evident in the ever-more-flowing lines of the newest Chevrolet Camaros and Pontiac Firebirds.

The Litestar, meanwhile, melds elements of motorcycle and car in an improved aerodynamic shape. It will, in fact, be licensed as a motorcycle in most states.

The vehicle uses a motorcycle engine and has two main wheels, one in front and one in back. Two ''outrigger'' wheels, mounted in spring-loaded wings, touch ground only on turns and when the vehicle is stopped. While cruising straight down the highway, the Litestar rides on the two main wheels.

Mr. Leitner says there's a ready market for his ultra-efficient vehicle. The company has factory-direct orders for 1,500 vehicles, plus 14,000 earmarked for dealers during the first year. The price is about $4,000.

The Tomorrow Corporation isn't the first small manufacturer that has tried to crack this market. Beginning in 1979, H-M-Vehicles began selling an odd-looking three-wheeler called the ''Free-Way,'' which got 100 m.p.g. at a steady 40 m.p.h. But, after selling 700 vehicles, the company went broke last summer.

In the drive toward high mileage, Detroit's auto establishment tends to view projects like the Litestar and the H-M-Vehicle as unusual hybrids, rather than serious competition.

''We've concentrated on getting high mileage from our smallest production cars, not from closed-in motor scooters,'' says Thomas Walsh, director of Ford Motor Company's vehicle-concepts research laboratory. ''But that isn't to say we haven't done studies on that approach, too.''

Nearly every major automaker is experimenting with an array of high-mileage models. Some even build sleek prototypes to test innovative ideas. But most designers agree a marketable 100 m.p.g. car is still years down the road.

''We're trying to project ourselves into the next decade and decide what a car will need to look like then,'' says Thomas Ankeny, project manager for General Motors Corporation's ''two-passenger commuter,'' or TPC, project. GM recently built a prototype vehicle capable of getting 95 m.p.g. on the highway.

The TPC uses no exotic metals or plastics and weighs in at a scant 1,040 pounds - about a third that of a Ford LTD. Besides trimming off automotive flab, the TPC's weight is further reduced by using a steel and aluminum alloy for the engine casting, as well as aluminum in the fenders and hood.

But, according to Mr. Ankeny, it will be at least the end of the decade before a car such as the TPC is produced. The biggest snag: All the parts are experimental and would require years of development before going into production.

Even if produced, the car probably wouldn't measure up to current highway safety standards. Ultra-high-mileage cars usually have difficulty passing crash-impact tests and minimum noise and vibration-level requirements.

''The bottom line, of course, is how much of what you've achieved on an experimental vehicle is realistic for production models,'' says Ford's Mr. Walsh.

For instance, one of Ford's suppliers developed a tire that significantly reduced the rolling resistance of the rubber against the pavement, which could have helped improve mileage. But the cost of producing the new tires, Walsh says , made them impractical.

''We go after every energy user on the vehicle,'' says Walsh, ''down to the bearings and seals - it's all specially designed.''

Ford builds an experimental high-mileage vehicle about once a year. One of the latest is the four-passenger Probe IV, which looks like something that took a wrong turn off a science-fiction movie set. Most of the company's research is done by adapting standard production models.

Not surprisingly, foreign automakers also have their eye on the ultra-high-mileage market. For example, Volkswagen has the Auto 2000, a four-passenger car it says gets at least 75 m.p.g. on the highway.

Renault, meanwhile, recently announced its new VESTA experimental car. This vehicle is supposed to meet the same standards of performance, comfort, space, and safety as Renault's boxy but economical Le Car. Its projected fuel economy rating is more than 85 m.p.g.

But like their American counterparts, French and German automakers plan only to integrate lessons from their ultra-high-mileage cars into future models.