If there is such a thing as a sleeper on the American automotive market, it is the Legacy sedan from Subaru of America.

Subaru, whose parent shares the Subaru-Isuzu Automotive Inc. plant near Lafayette, Ind., offers in the Legacy an automobile that utilizes state-of-the-art technology and adds a few touches of its own.

Principle among these is Subaru's opposed-4 and opposed-6 engine configuration. More commonly known as a flat-4 or flat-6 in the automotive trade, the concept is not in universal use among the world's automobile manufacturers.

Automakers may have overlooked a good thing. The opposed-cylinder layout offers advantages like an inherent balance of an engine's reciprocating componentry, and a low frontal profile.

Subaru's Legacy goes further by incorporating advanced four-wheel suspension, manual or automatic transmission systems, optional comfort and convenience systems, and interior styling themes that make a midrange-priced four-door look like a more-expensive car.

The Legacy runs from standard to upscale, with a moderately equipped L model representing the broad range of the series. It has a moderate base price, and you can go from their in equipping the compact.

The Legacy L that Rick Shewmake, general sales manager of Speedway Volkswagen-Subaru, provided for a test car drove and acted like a fairly powerful midsized car. Thanks to a 16-valve flat-4 that put out 130-horsepower, the sedan exhibited quite acceptable performance for a car this size.

The engine in this machine activated the four valves per cylinder via a single-overhead cam on each bank rather than by the traditional dual-overhead cams. It leveled off momentarily around 30 to 33 mph on full throttle off-the-line runs, but then came on with a good power surge and gave the car excellent acceleration.

The ease of the ride for a rather light sedan will catch everybody's attention. The ride almost floats, but without body wallow on fast turns. Subaru's suspension engineers have found a good balance between spring rates and stability.

Likewise, engineering has done a respectable job on interior room, considering it was dealing with 177.6 inches of overall length. The sedan will carry five people, but four is a more feasible number for comfort.

Amoung the test car's options that contributed to driving pleasure were air conditioning, automatic transmission and cruise control. Obviously, they push up the cost, but the satisfaction remains long after the price is forgotten.

A couple of individual touches that other mass producers could follow was a driver's side window that automatically went up as well as down and a manually oriented memory tilt wheel that automatically returned to its preset position.

In all, the features made the L an upscale car without resorting to upscale prices. That should continue to enhance its market position.

1991 Subaru Legacy LBase price: $12,924.As tested: $15,896.Type: Front-engine, front-drive, f ive-passenger compact sedan.Engine: 2.2-liter, 16-valve, fuel-injected, four-cylinder.Mileage: 21 mpg city, 28 mpg highway.Acceleration: 0-60 mph in 9.6 seconds.Length: 177.6 inches.Wheelbase: 101.6 inches.Curb weight: 2,830 pounds.Options: Air conditioning, automatic transmission, power windows/locks, 80 Watt audio/w graphic equalizer, cruise control, special paint.Area dealers: Speedway, Tom Wood.