Detroit is beginning to get the message.

Car manufacturers are wondering out loud whether their product really has to be loaded with chrome and bulges to have domestic sales appeal.

A few '79 models are already sporting a "European look." They show clean, functional design.

It has long been a platitude that, ever since they traded the Model T for built-in obsolescence, American car manufacturers "styled" their products rather than designed them. The fewer technical changes they make in the annual parade of "new" models, the more gimmicks and meaningless frills -- like fake air scoops and merely ornamental grilles -- they put on.

Lewis Mumford once said that the automobile is America's pampered mistress. Detroit stylists seem to believe that the American male likes his mistress done up like a tart. only rich people were supposed to fancy good, chaste design, like Barcelona chairs and "continental" Lincolns.

The tart look never sold abroad, although foreigners tend to be just as infatuated with cars as we are. But American Motors, for instance, strips its Jeeps of splashy chrome and gaudy graphics before it is shipped to Europe. Germans who purchase the most expensive Mercedes, wrote Del Coates in a recent issue of "Industrial Design" magazine, are so anxious not to appear ostentatious that they will remove the identifying "450 SEL" from the trunk soon after delivery and either fill the holes or replace it with a less prestigious "230."

Coates, who teaches automotive design-engineering in Detroit, has revived the old-fashioned word "concinnity" to define "good design" of automobiles, or anything else, for that matter. The word unifies two disparate streams of esthetic thought, says Coates, to explain why the word is useful to him.

One is the Platonic notion that beauty is strictly an objective matter, that every object has some perfect, ideal form which, once discovered and expressed, will have universal appeal.

The other view is that beauty rests within the eyes of the beholder, that it is entirely subjective and personal, depending on thoughts, feelings, beliefs, ideals, social objectives and, of course, the Zeitgeist .

Concinnity, says Coates, is usually considered synonymous with "harmony" or "elegance" and occasionally, but inaccurately, with "beauty."

What it really means, according to Coates, is the same as the Latin "concinnitas," or "well put together." A Roman senator's speech was considered concinnous if it not only sounded good to the ear because of its intonation, but also exalted the mind because of its logic.

Applying this definition to automobile design, Coates says "concinnity occurs when there is a close harmony of the car's objective form -- the form that follows its function -- and the subjective meanings associated with the car."

In other words, lines, shapes and forms meet the car's technical requirements without exaggeration, distortion, fakery or gimmicks, and are also designed in such a way that they meet the buyer's psychological expectations of what a good car ought to look like.

These psychological expectations change from one culture to another and from one time to another, because of different experiences and concerns.

The European expectation of a car, to venture a generalization, is mostly technical efficiency. Owning a car in Europe is in itself a symbol of wealth and status. What the German, Italian or Frenchman expects of the car is not that it dazzle his neighbors, but that it serve him as a reliable precision instrument. The designer's job is to reinforce this expectation.

In America, owning an automobile is no big deal. It is an essential life support. Americans, furthermore, used to take their technical superiority for granted. They wanted romance, novelty and luxury. Responding to this urge, the stylists tried to make their car appear to be a big deal, something lush and dazzling.

"As a result," says Coates, "American car designs are one step removed from reality. They are based on images of things, not on the things themselves. A highly placed automotive product planner once told me in all seriousness that 'the product planner's function is to find out what the consumer thinks he wants, and the designer's function is to make the consumer think he's getting what he thinks he wants.'"

European car designs, responding to functional needs, tend to provide an incentive for manufacturers to introduce functional improvements.

Coates emphasizes, however, that the difference is not between American and European designers, but between American and European marketing directors. "There is little difference in the way good designers think and act, regardless of where they happen to live... European design is nothing more than good design..."

A good design is beginning to infiltrate Detroit. The studios and even a few board rooms are in a European mood, tending toward what Coates calls "objective concinnity."

What has happened is, first of all, that Americans are increasingly exposed to good European and Japanese car design and are beginning to appreciate it. With what the automobile industry calls "downsizing," the distinction between European and American cars is no longer predominantly one of size, but of design. But imports continue. In some California communities more than half the registered cars are imports.

Another factor is the growing demand for energy efficiency.

In large measure, European cars look the way they do because energy efficiency has always been of great importance in Europe. The price of gas has consistently been higher than in the United States.

Energy efficiency means lighter cars (which, contrary to popular belief, does not mean that they will be harder to handle and thus less safe than heavy cars). And it will mean a better understanding of aerodynamics and the need for simple and smooth surfaces.

A good beginning is the '79 Ford Fairmont, which, as Coates put it, "has more objective concinnity than most American cars -- due mostly to its relatively straight lines and flat surfaces, lying in essentially horizontal and vertical planes."

Typically American, in contrast, is the Chevrolet Monte Carlo, which Coates describes as "a collection of ill-fitting curves, surfaces and other elements. Consequently, it is very active, or, more precisely, nervous or busy. Little European flavor here."

Not just in cars, in all mass-produced objects, the European flavor is beginning to appeal to the American taste. CAPTION: Picture, The Mercedes 280E, left, and the 1979 Ford Fairmont