In all the twittering over Lexus and Infiniti, accompanied by some defensive snorting from Mercedes and BMW, one vital fact seems to have been ignored: Cadillac is still America's best-selling luxury car.

Cadillac's hold on that title has remained unbroken since Gandhi was assassinated, cancer struck out Babe Ruth, a Jewish state was born, Truman became President, LPs spun for the first time and a doctor named Ferdinand built something he called the Porsche 356--all of which was 42 years ago.

In the just-concluded model year of 1990, Americans bought 258,000 rolling sofas by Cadillac--a sales total larger than the combined sales of Lexus, Infiniti, Mercedes and BMW.

Last week, the U.S. Commerce Department's Malcolm Baldrige National Quality Award, corporate America's desired recognition for excellence of production and product, went to Federal Express, IBM, Wallace Co. (a small petrochemical firm in Houston) and General Motor's Cadillac Division.

And the 1991 Sedan DeVille--almost two tons of cushioned comfort, close to 17-feet of gadgets that do much of a driver's thinking--is total justification for the Baldrige.

Here is a car--whether you disembarked at Ellis Island or were born in Des Moines--that continues to look and feel like old money and remains the model for having Made It In America.

Every American President since 19 naught whatever has ridden in a Cadillac. It has been the vehicle of choice for ticker-tape parades, Wall Street before the Depression, most of early Hollywood, William Randolph Hearst, Burt Reynolds, Al Capone and Saddam Hussein.

"We do sell image more than a product," said Cadillac spokesman Chuck Harrington. "And we sell lifestyle."

Cadillac's current lead in the luxury car and lifestyle league, he continued, is retained by the division's reputation for quality, reliability and prestige, "whereas Lexus and Infiniti have still to create image and a history."

Harrington also believes there is"a fairly strong undercurrent" building for Buy American.

The new DeVille's three cigarette lighters, carpeted litter bin, automatic parking brake release, front cornering lights and turnpike change container leave no doubt of its country of origin. Nor of its special transportation service provided quintessential customers: Older Americans with several bank accounts and no need to do their own tuneups.

Driving the car is an exercise in transmogrification. After 10 miles, there develops an urge to buy a condo in Palm Beach. After a day, one is ready to discuss big band music with Don Ameche.

At the same time, however, motoring in a DeVille brings a unique silence for private thoughts. Also a softness for any part of a body that must contact interior portions of the car.

The leather upholstered seats are front-parlor. Save for the ponderous turn-signal lever, control functions are mostly fingertip and feat her touch. Indeed, the hard work of driving seems left for those unfortunates buzzing around in Mazdas and Ford Probes. On the safety side of things, a driver's side air bag is standard on all 1991 Cadillacs. So are anti-lock brakes. But the best horn in all of motoring--something that sounds rather like a bull moose swallowing a freight train--remains part of an option package.

As for size and interior room, the Cadillac style is not to slip people into a capsule resembling a form-fitted bathtub. Rather, it supplies the entire swimming pool and allows you to find the most comfortable lounging position.

Headroom is for tall diplomats in stovepipe hats. There is less leg and elbow room in a small gymnasium. Some cars are designed to nip and skip around similarly moving objects. The Cadillac is built to stay put and bounce offenders to Bakersfield.

In absolute contrast to this sturdiness and bulk--and with total credit to its chassis designers--the D Ville does not maneuver like a huge car. Nor does it give that wallowing and pitching in traffic that came with Cadillac's earlier aircraft carriers.

Oh, the suspension is soft and the steering somewhat anesthetized. That, of course, is the American Luxury Car Lollop.

But now there's a computer monitoring Cadillac's suspension and ordering up comfort-normal-firm damper settings, depending on speed, ride and road conditions. The power-assist on the steering has been dialed back, and there is a tighter turn-in with less of that old sense that the rack-and-pinion system was attached to four jellyfish.

Yet do not believe for one moment that the handling and performance of the DeVille is on a par with Lexus and Infiniti. Nor does this particular model feature the old-world dedications to durability of fittings, burled walnut and polished titanium of Mercedes and BMW.

But those imports are tuned to a younger, faster clientele that prefers to bond with its cars. Lexus, Infiniti, et al, also cost many thousands of dollars more. Visually, the 1991 DeVille follows Cadillac's continuing retreat from Coney Island chrome and styling trims that always seemed to emphasize length and beam. There's a new decorum to the whole, almost the big Mercedes look, with side cladding that gives the car a more slender appearance, and a set of very handsome cast-aluminum wheels.

Even Cadillac's laurel wreath and crest emblems seem to have been downsized until they assume the discreet position of styling accents, not body jewelry.

The interior is elegant and familiar, even the digital instrumentation, which has been considered froufrou and hopeless Detroit glitz on other vehicles.

And there are those pleasant little touches--the radio that turns itself off when the driver's door is opened, the cup holder that flips out of the arm rest, the parking brake that pops off when the gearshift is put into drive, instrument lights that come on automatically in dark garages--that have always been Cadillac at play.

But height adjustment is needed for shoulder belts permanently mounted at precisely the right height to rasp anyone's jugular. Thanks to a driver's side air bag mounted in the lower portion of the steering wheel, the dash is blocked out (particularly annoying when trying to select drive from park) whenever the wheel isn't at top dead center.

We were never able to fathom all the permutations of the central locking system. That meant consistently leaving the car with the driver door secured and the passenger doors unlocked. At one point, from inside the car, every combination of switch and key was unable to release one door--much to the frustration of the passenger behind that door.

Amid all its traditional trickery, however, Cadillac has not seen fit to install a headlight flasher for daytime signaling. Nor has it filched that wonderful system of popping the trunk and ga s cap by remote control--with the engine off.

And here's a complaint you don't hear too often:

The car is slightly overpowered. This year's engine has been enlarged from 4.7 liters to 4.9 liters, with a 20% increase in oomph to 200 horsepower. Torque has been improved to 275 foot-pounds. That's getting pretty close to the maximum amount of power anyone wants to feed front-driving wheels.

It translates to acceleration times that are quicker than a Jaguar V12, the Peugeot 405 Mi16, the Isuzu I Mark Turbo and other sports.

It also means that beneath a heavy hoof, this dreadnought will perform some interesting takeoffs if the front wheels aren't pointed dead ahead. That is not something that would seem to fit the fascinations of Cadillac's median customers.

Unlike other manufacturers and divisions of General Motors, Cadillac is not interested in serving anything but the luxury car market. It does not make sport utility vehicles. We will nev r see a Cadillac van.

Pity. Some young Californians have long had their ambitions set on a Cadillac pickup. To be marketed as the El Dorado El Camino.

1991 Cadillac Sedan DeVille

The Good Luxury Yankee Doodlemobile. Suspension with improved muscle tone. Less pizazz to styling. Quality look, feel and ride.

The Bad Too much power. Steering wheel design. Garroting by seat belt.

The Ugly Visually unbalanced steering wheel.

Cost Base: $30,455. As tested: $34,447 (includes security package, power seats, Delco-Bose sound system with CD, leather seats, illuminated vanity mirrors and other options).

Engine 4.9-liter V-8 producing 200 h.p.

Performance 0-60, as tested, 9 seconds. Top speed, estimated, 125 m.p.h. Fuel economy, as tested, city-highway average, 20.5 m.p.g.

Curb Weight 3,545 pounds.