MEDIOCRITY HAS MERIT. The 1986 Chevrolet Celebrity Eurosport sedan is proof.

Yeah, 1986. I rented it from National Car Rental on a recent business trip to Indiana. Drove it several hundred rainy miles. An absolutely ordinary, devotedly suburban, passionately middle-class, American family car.

I was impressed.

Manufactured in March 1986 and sold to National shortly thereafter, the Celebrity Eurosport had 21,000 miles on it when I picked it up. It also had several scratches and a few dings on its dark metallic blue body; and there was some minor vandalism -- a missing plastic "Eurosport" nameplate, torn from the interior panel of the driver's-side door.

Mostly, though, the car's appearance was passable. Bland, linear styling inside and out, but nothing terribly offensive or bothersome. Sort of an automotive Levittown.

A slam? Nope. Lotsa families grew up in the Levittowns of America in comfort and safety. Judging from the performance of the rental car, lotsa families in Celebrity Euro- sports get around the highways of America in pretty much the same way.

Complaints: Surprisingly few. There were some rough spots in gear changes in this four-speed automatic transaxle, front-wheel-drive car. But the ill-mannered vibrations were infrequent and short-lived.

Also, I could live without the non-reclining, cloth-covered front bench seat. Bucket seats are preferable for this bottom. Of course, not all bottoms are created equal.

Praise: You hear so much hype about the inherent superiority of Japanese and German cars, you almost start believing it. Indeed, the "Eurosport" marketing of the Celebrity is a product of that silliness. Too bad. This All-American folksmobile is good enough to win on merit.

Any car that retains dignity and composure after 21,000 miles of brutality from scores of different drivers gets my vote. Fit and finish on the Celebrity Eurosport held tight. Egads! The climate control system -- air conditioning and window defrost -- worked better than those in several far more expensive, 1987 Japanese and German cars.

Braking worked well on rain-slick roads. But some credit here goes to the original equipment, steel-belted, Uniroyal Tiger Paw radial tires, still gripping after all those punishing miles.

Ride, acceleration and handling: Good. In fact, notable, considering the Indiana-Ohio downpours that turned the test drive into a scary kind of water torture. The Celebrity Eurosport maintained normal highway speeds without slipping, sliding or shimmying. The steadiness of the ride bolstered confidence.

The car's standard 2.5-liter, four-cylinder, fuel-injected engine whined a bit at higher speeds. But it pulled its weight.

The 1986 Celebrity Eurosport standard engine produces 92 horsepower at 4,400 rpm, compared with 98 horsepower at 4,800 rpm produced by the improved 2.5-liter engine in the 1987 model.

Sound system: AM/FM stereo radio, electronic seek and scan, by GM/Delco. Better tonal quality and signal retention than many brand-new auto radios.

Mileage: Easily 25 to the gallon (15.7-gallon tank, 390-mile range), driver only (with about 50 pounds of luggage), mostly highway and air conditioner on most of the time.

Note: With the exception of the improved 2.5-liter engine and a few touchups on exterior styling, the 1987 Celebrity Eurosport's practically identical to the 1986 model, which should make the next paragraph interesting.

Price: $8,400 by National Car Rental's used-car division. Price includes air conditioner, power steering and power brakes, and a two-year, 24,000-mile warranty from date of purchase on all powertrain and related drive components.

National, like its major competitors in the rental-car business, routinely sells its cars before they turn 30,000 miles. Detailed maintenance histories are available. Ask for them.

New-car price: $12,209 for a comparably equipped 1987 Celebrity Eurosport, includes $1,530 in options and $414 destination charge. General Motors new-car powertrain warranty is six years, 60,000 miles. Dealer invoice on 1987 model is $8,858.70.