The two advertisements, each full-page, only 10 pages apart, leapt at me from a recent issue of The Wall Street Journal. This national financial daily is a favorite advertising medium for automobile manufacturers aiming at tycoons, both imagined and real, and it is common to see promotions on its pages for such pricey makes as Rolls-Royce, BMW, Jaguar, Ferrari, Maserati and Peugeot. But this particular pair seemed to amplify an anomaly in the luxury-car market in the United States.

On one page was an ad for the Mercedes-Benz 300E sedan, led by a bold headline reading "Learn to love the Mercedes-Benz 300E the way the world's automotive experts did; by driving it." The text that followed carried extended excerpts from road tests in Car and Driver, Road & Track, and Car, a British magazine, all of which lavished praise on the performance and safety of the mid-size Mercedes. A bit farther back in the paper was an ad for Cadillac with the headline "Only Cadillac offers you a $2,000 bonus." The ad copy was a hard sell based on discount prices, bonuses and 1.9 percent financing for all six-passenger Cadillacs, including the DeVille, the Fleetwood and the Brougham.

The contrast was vivid. Here were two of the oldest and most honored automakers in the world hawking their wares, but in markedly contrasting styles. Mercedes-Benz, now entering its second 100 years, simply quoted a series of accolades. Cadillac, perhaps America's most honored marque, was reduced to fire-sale tactics to clear unsold inventory.

Statistics tell the story behind the ads. During the first eight months of this year, Cadillac sales dropped 18,376 units, from 192,946 during the same period in 1986. Mercedes-Benz sales in America fell by 1,740 cars, from 60,003 for the same period, partly because of higher prices. Mercedes-Benz has raised the price of the 300E, for example, from $39,500 to $42,570 this year alone.

Although Cadillac held the line on its prices -- already as much as $20,000 cheaper than Mercedes to begin with -- it still watched sales decline and its image fade. Its leading-edge products, the front-wheel-drive Seville, Eldorado and DeVille, absorbed the brunt of the slump. The one bright spot in the sales picture was the decade-old Brougham, an overweight ark that appeals to a consumer about 60 years of age. By contrast, the widely heralded Allante, an exotic two-seater based on the front- drive Eldorado and featuring a custom, Italian-built Pininfarina body, has been a disappointment. Less than half the intended 7,000 units have been sold, and some dealers are discounting the $55,000 price tags. (Martin Cadillac, the fourth largest Cadillac dealer in the nation, recently had 20 Allantes lingering on its lot in West Los Angeles.) The softness in Cadillac sales is further proof that the trend-setters in the luxury automobile market have abandoned the marque for European imports. Even Lincoln, Cadillac's arch-rival in the domestic field, is scoring gains. Sales of the big Mark VII coupes and four-door Town Cars were up by more than 5,000 during the same eight-month period (107,921 versus 102,407). In 1988 Lincoln will introduce a new Continental styled in the aerodynamic and highly popular Ford Taurus idiom while Cadillac must make do with a belabored face lift of the boxy current models.

The problem is quite simple. The current GM corporate administration, led by Chairman Roger Smith, has become a slave to centralization. Automobiles designed and styled by the corporation rather than by the five GM car divisions have become the much-maligned cookie- cutter products that give a Cadillac little or no distinction from a Buick or an Olds. But, as the song goes, the times they are a-changin'.

Cadillac's own managers have come alive. They have announced a more independent course, breaking the lockstep that has linked them with lesser GM divisions. There is talk of radical changes in the early 1990 models, with a V-12 engine leading the comeback. Cadillac's great cars of the 1920s were powered by V-12s and V-16s, and there is widespread belief that the new, exotic engine will be a boost for the car's mystique. (V-12s are very much in vogue these days, with BMW having just introduced such a power plant for its excellent new 7-series luxury sedan. This has forced Mercedes-Benz into a frantic program to get to market with its own V-12 by 1991.)

Cadillac engineering types also talk openly of four-wheel-drive, computer- controlled active suspensions that change as the road and driving situations change, even four-wheel steering. This is cause for hope.

What Cadillac needs is a product that at least matches the best from Europe in terms of quality and performance. This means a four-passenger automobile, a` la Mercedes-Benz and BMW, that will develop more than 300 hp, run 150 mph, corner like a Grand Prix car and contain every known safety advance from anti- lock brakes to state-of-the-art passive restraints. Thankfully, it's not too late. Cadillac, created in 1902 by Henry Leland (who later founded Lincoln), has one of the great heritages of the industry. It was in the forefront of such automotive advances as the self-starter, electric light, synchromesh transmission and high-compression V-8 engine. The highly regarded J.D. Power Consumer Satisfaction Index for 1987 ranked Cadillac as the best American marque (seventh overall, behind Acura, Honda, Mercedes-Benz, Toyota, Mazda and Subaru, but five places ahead of rival Lincoln). Recovery to its former ranking among the world's great automobiles ought to be relatively easy, providing General Motors management is willing to invest the funds and the engineering brashness to propel it onto a new technological plateau.

I wish Mercedes-Benz no ill, but for the sake of us all, as consumers and as citizens of a nation being sapped by a sagging industrial image, it would be wonderful to see Cadillac once again build the world's best automobile. ::