IT WAS a secret mission, code-named "XX" -- a collaboration between Japan's Honda Motor Co. and Britain's Austin Rover Group.

The objective: "Build two distinctively different cars from the same mechanical base."

Mission accomplished. Too bad for Honda. Austin Rover did a better job.

The proof is in the products -- the 1987 Acura Legend sedan marketed by Honda and the 1987 Austin Rover Sterling 825SL sold in the United States by the Brits' American partner, Austin Rover Cars of North America.

Both the Legend and Sterling are front-wheel-drive machines sharing the same engine and transaxle developed by Honda. Both cars have the same basic body structure developed by Austin Rover.

But on matters of suspension, exterior and interior styling -- the things that help define the personality of a car -- the two auto makers went their separate ways. And Honda got lost.

The Legend emerged as a technically perfect bore, a tendentious neurotic in hot pursuit of predictability. This car requires both an ignition key and wedding ring to get going.

But, ah, the Sterling! Here's the passion the Legend lacks. Here's the thrill of being behind the wheel of a first-rate cruiser.

Austin Rover knows how to put feel into a car. Look at the Sterling's interior: Rolls-Royce Connolly leather where the Legend has plastic, velour or workaday rawhide; laminated burled walnut where the Legend has nothing.

And on the outside, the Sterling is graced with clean, snappy lines, whereas the Legend is content to pay homage to the rounded philosophy of Audi and other German auto makers.

Ah, and this, silly as it seems: the Sterling sports a real, eye-catching badge in the external places where the Legend merely announces the number of cylinders and valves installed in the car.

It's no contest. The Sterling wins hands down. Sterling, this column's for you.

Complaints: Exposed electrical wiring harnesses underneath the Sterling's front power seats. Tacky. With all that Austin Rover has done to this car, the company certainly could find a way to hide those wires.

Also, the Sterling's hood release is mislocated on the lower right, front interior wall. Austin Rover will change that. Good. Hood-release hatches should be on the driver's side, the left side of cars sold in America.

Praise: An all-around good, classy luxury car. Generally top-rate craftsmanship.

Head-turning-quotient: Show stopper. People rolled down their windows to ask about this one. Nobody did that for the Legend.

Ride, acceleration, handling: Triple play. All excellent. The Sterling 825SL runs with a 2.5-liter, 24-valve, fuel-injected V-6 that pumps out 151 horsepower at 5,800 rpm, same as in the Legend sedan. (The Legend Coupe is fixed with a 2.7-liter version of this engine, producing 161 horsepower at 5,900 rpm.)

The Sterling's ride is firmer than that of the Legend sedan and Coupe. Better, too.

Sound system: Eight-speaker AM/FM stereo radio and cassette, by Phillips. Superb.

Mileage: About 23 to the gallon (18-gallon tank, 414-mile range), mostly highway, running driver only and with air conditioner on most of the time.

Price: $24,580, including $295 in options and a $385 destination charge. Base price is $23,900, several hundred dollars less than the comparable Legend sedan (with four-speed automatic transaxle). Dealer's invoice price on the Sterling 825SL is $21,014. But most dealers aren't dealing on this one.

Warren Brown covers the automotive industry for The Post.