Consider the horse. Has anyone up to now given any real thought to the cultural contributions of that magnificent creature? Recognition seems long overdue.
Belated or not, full honors are now being paid in a major exhibition at the Metropolitan Museum of Art. ''Man and the Horse,'' the new show installed in the museum's Costume Institute, is a stylish salute. Conceived by Diana Vreeland, the institute's special consultant whose highly popular annual productions are always done with admirable flourish, the exhibition is a departure from her previous more fashion-oriented shows (such as last year's celebration of the accomplishments of Paris couturier Yves Saint Laurent).
Although the current exhibition, which runs from Dec. 18 through Sept. 1, 1985, may seem to be tackling a broader theme, it makes no try at an in-depth survey delineating the economic and military role of the horse. Mrs. Vreeland's scope, as might be expected, is rather contained. It lies within social, artistic, and ceremonial boundaries, accenting the view-halloo, boots-and-saddles lore of horsemanship.
''Men and women never look as good as they do in their riding gear,'' she says in her introduction to the illustrated book the museum has published for the exhibition. ''The fit of the boots, the white suede breeches and racing silks, the saddle blankets thick with embroidery, the silver, gold, and bronze spurs, and bits oiled and polished. . . .'' In the equestrian world, as she sees it, ''One dresses down to perfection.''
The point is made in the museum's galleries in various ways. A tack-room display of burnished equipment, blankets (including one with the insignia of Queen Elizabeth II), and elaborate saddlery (that of Louis XV, for instance, circa 1700) sets the scene. Tableaux of immaculately turned-out mannequins in the black, hunting pink, or beige habits worn by proper riders of yesterday and today are reminders of the disciplined tailoring originated by the sport.
The point was reaffirmed on the night of the gala black-tie preview when some of the men, from the Middleburg and other hunts, arrived in their evening scarlet coats. Greeted with admiring ''oohs'' and ''aahs,'' they completely outshone the women in their Saint Laurents and Givenchys.
The show harks back as far as the 16th century, when both knight and his mount were armored in gleaming steel. It explores coaching, polo playing, thoroughbred racing, and the Far West (the beaded buckskin jacket Buffalo Bill wore, for example), among other aspects of equestrianism - from sporting vehicles and stately carriages to artworks.
There are the uniforms of the Spanish Riding School of Vienna and the Cadre Noir of the Ecole Nationale d'Equitation of Saumur. There is the habit of Olympic gold medalist Joe Fargis. And there is the red Spanish Feria outfit designed for Mrs. John F. Kennedy. ''It is a riding-for-pleasure and a riding-for-sport show,'' says Jean R. Druesedow, associate curator-in-charge.
The impact will no doubt be evident in next fall's clothes and accessories, when horsy tattersalls, covert cloths, starched white stock ties, harness brasses, and such are likely to constitute a galloping trend.
But fashion has long been in debt to the equestrian mode. The evolution of sportswear as we know it can be traced to early riding clothes. Hacking jackets made by such designers as Ralph Lauren (whose company, Polo/Ralph Lauren, contributed $350,000 to sponsor the Met show) are direct descendants of the attire worn by 19th-century Amazones. The tailored suits favored by modern-day businesswomen also have the same fashion lineage.
''Riding apparel gave women in the 17th, 18th, and 19th centuries the opportunity to wear simple clothing styled like men's - down to the pocket flaps , cuffs, buttons, and buttonholes,'' Ms. Druesedow says. Those elements still exist in today's sportswear.
Except for a few historic cases (Jean Druesedow cites the Wife of Bath, Joan of Arc, and Diane de Poitiers), riding aside was the rule through the ages for women on horseback. Only the most daring ventured wearing breeches instead of perching sidesaddle in an apron skirt. ''Riding astride did not become popular until the late 'teens and early 1920s,'' says Ms. Druesedow. ''Chanel was an influence. She borrowed the habit of one of her men friends, then made herself a copy of the jodhpurs that belonged to a groom.''
The art assembled for ''Man and the Horse'' is especially fine, including Degas bronzes and works by all the great horse painters - Delacroix, Stubbs, Raeburn, Herring, Munnings - plus a small Gericault oil of a roan dray (the only workhorse in the show). Of particular interest: the Louis Auguste Brun portrait of Marie Antoinette on her black mare. In dashing plumed hat and pink coat, she wears breeches under her skirt and is riding astride, which tells us how forward-minded she was - in some respects, at least.