When Catherine de Medici was ruling France from a bankrupt throne, desperately trying to unite a country split, demoralized and impoverished by religious war and threatened by the power of Spain, she mounted extravagant festivals at court at carefully chosen moments. These required sumptuous dress for everybody, with expensive fireworks and professional entertainment celebrating the strength of the crown and the peaceful harmony of Catherine's court could come away with a distinct sense of French wealth and French self-confidence, despite grim evidence to the contrary in the country at large.

Sixteenth-century methods are far from obsolete, as we can see from the recent inaugural display featuring well publicized parties with fireworks and fine clothes, and carrying the suggestion of confident policies no matter how sobering the situation. The amount of public attention to the Reagan festivities, combined with the eclipse of the Carters well in advance of the event, suggest that the American people rushed to elect not just the man but the manner, and that Carter lost because his had gone unforgivably out of fashion. Anxious concern, caution and doubt, however justified, are evidently not what Americans wish to see visibly mantling the presidency: we want it wrapped in mink, flashing smiles and diamonds and riding in a limousine before the eyes of the world.

The much-vaunted "style" allegedly sweeping Washington and now representing the nation is nothing new -- it is only new in Washington. Luxury has many possible flavors; and this particular style of wealth has a somewhat dated cinematic aura, ladylike and gentlemanly in the simplistic manner of movies before explicit sex, drugs and Vietnam, when rich middle-aged people all had perfect hair, perfect clothes, perfect figures and fixed smiles. All suggestions of distinctive ethnic background, all specific cultural attributes were wholly muted by celluloid Middle Americanness in the upper-bracket mode. It is in fact an ideal palpably realized in many western and midwestern American cities, although not so conspicuously in New York, where the most noticeable rich come in saltier flavors.

Standard American riches never have comfortable connotations either of exuberant upstart vulgarity or languid aristocratic decadence, and empathically no trace of European ambiguity and perverisy. The trappings of this particular sort of American success have a slightly denatured quality, pointedly wholesome and accessible to the broadest scope of the public imaginatioin, undisturbing and unsuggestive in any complex way. They connot a comfort that extends to marital harmony and genial decorum in family conduct, and opulence without raciness. All this is expressed in the kind of festal array lately sported in Washington. The clothes worn by Mrs. Reagan and the other ladies of her circle show a decent lack of startling originalty or unnerving personal quirk. They look very expensive without suggesting any other forms of license; and they are worn with no aggressiveness or apology, nor with contemptyous indifference, but with a certain conscious pride.

But the fashion for clothes bearing simliar connotations was well under way before the recent presidential campaigns. A general conservatism has been strengthening its contribution to the flow of fashion for some time, notably the mode in business costume for ambitious women -- the expensively tailored Wall Street suit -- and in accedemic costume for the young -- the "preppy look." These particular genres have East Coast origins but nationwide repercussions. Denim, that overwhelming ocean of plebeian blue, has slowly and almost unnoticeably been polluted. It has gradually lost its purity, its zeal, its moral luster, its character as Worthy Opponent, and a great deal of its tidal force. When denim finally hit the White House, the tide had already turned. By insidious stages, in a long-range maneauver implemented by designers and the media, blue jeans have become Establishment fashion. The daring and controversial new mode is expensive, formal garments.

About two decades ago, galloping informality overrode the nation and occupied it from coast to coast, affecting all groups. Respectable women began to boast of owning no dresses, serious professors gave up teaching in jacket and tie, the young wore old rags, hats vanished. Finally, all defense for the virtues of formality in dress fell before the profound appeal of the Counterculture Costume in all its infinite variety. This ranged from nudity on up through all degrees and overlapping suggestions of historical, rural, technical, theatrical, ethnic and infantile gear, sometimes laced with indications of morbid sexual preoccupation. The fashion business kept pace with all this, offering slick versions of sleaziness, crudity and bizarrerie accompanied by persuasive prose featuring "freedom." On the street, jeans held the whole thing together, uniting young and old, imaginative and dull, crummy and flashy. Carefully designed, well-made, complicated and demanding formal clothes went into eclipse, and their adherents into fashion limbo. The Reagan style of riches aliso left the spotlight, though never the stage. It was known to be flourishing, if only to stand for the square conservative culture against which all the modish and well-publicized freedom of expression was steadily aimed.

This stylistic situation had its obvious sources in the state of national and world affairs at the time. Nowadays, although it might be said that the condition of things has not vastly improved, it has changed, and an eagerness now apparently exists for different expressive material. We are not going back; we are going ahead on a predictable path.

After any sustained period of diffuseness, diversity and haphazardness in dress, the need for formal order reasserts itself in some way. Since costume is not a primitive art, most of its phenomena do not have easily read one-to-one correspondences with political events -- they have a certain formal autonomy. The trend toward sartorial formality, already in motion for several years, would have triumphed in some fashion under a Democratic president. So perhaps would the novel impulse toward a conventional display of wealth: many famous Democrats have been seen to wear fur coats. An adversary spirit can become a tedious burden in clothing, especially after it has won. When former president carter appeared before the nation in his famous sweater, the sharp reaction already signaled a certain boredom with such expressive devices; and canny observers might have predicted that he would lose to somebody who seemed more prepared to wear white gloves.

We also seem in a mood to relish news of outrageous expenditure. Gasping at the money paid for works of art has certainly been a public pastime for some years and inflation has made the prices of many familiar things into a hideous, near-hilarious absurdity. One thing about elegant costume -- you can see where the money goes. Fur and embroidery and luxurious fabric, careful design, perfect tailoring and hand-finishing all have an obvious right to be expensive. In the strictly informal mode, the display of wealth has to confine itself very carefully, and it can end up in the form of $400 blue jeans and skimpy minimal shirts hugely stamped with famous designers' names. Such distortions eventually produce an effect of strain on the casual scene, an ease beginning to show unease. Reactions are also ambivalent and uneasy. By now the effect of inflation on luxurious clothes and accessories has made them almost mythically costly. Publicizing their prices, as in connection with the recent celebrations, increases their already legendary glamour. It can give an old-fashioned kind of satisfaction to the watching public, of which a large part may come from expresing good old-fashioned indignation.

One other attraction in the new presidential style may be that it generally reflects the taste of older people after all these relentless years of youth. Perhaps, as the number of citizens over 60 increases and can be inspired by such a glittering ideal in the White House, our younger Americans may at length wish to copy their elders, instead of the other way around.