COOPERSTOWN, N.Y.— The New York State Historical Association, perched over Lake Otsego, the Glimmerglass of James Fenimore Cooper fame, is celebrating its centenary this year. And the big 1930's neo-Georgian headquarters it calls home is stacked to the attic with exhibitions of American art.

Together they stake out a wide territory, ranging from 19th-century landscape painting to 20th-century rural crafts to spectacular American Indian work. And in the largest and most ambitious show on view, ''Empire State Mosaic: The Folk Art of New York,'' all these elements play a role.

Folk art was once a catchall term for handmade things, preferably of rural pedigree, that strayed out of the fine art range. The concept has been rethought in recent years, and breakaway categories like outsider art have assumed a life of their own. But at Cooperstown the umbrella concept is still in place, and it works well enough for most of the material included here.

In essential ways American art has always been about folk, plain people, what they know and want and value, though for a long time art history offered a different picture. It saw American culture as an upstairs-downstairs affair, with an unbridgeable gap between high and low. Elite art, which often meant European art, might descend from above to inspire popular responses, but the process didn't flow both ways. Few people buy that view now. True, European forms were assiduously copied, but they were also smartly retooled, turned into something different: simpler, wilder, desirably new. Provincialism meant rejuvenation as well as imitation, fresh impulses born from old roots in new soil.

Newness was, of course, built into the American situation, and it left all kinds of esthetic ideas and alliances up for grabs. Art and advertising quickly joined forces. When Progress became a hot national concept, artists promoted it through images of railroads, boomtowns and the Erie Canal. And in a culture where social distinctions were fluid, portraits created people, rather than the other way around. If the likeness you commissioned made you look like a gent, you were a gent.

At the same time, anything highfalutin went against the grain, and no art form or theme was sacrosanct. Landscapes appeared in paintings, prints and pay-at-the-door panoramas. A marble sculpture of George Washington and a cigar-store Indian struck the same noble, eyes-to-the-skies pose. Even 19th-century Native American art conformed to the pattern, as Indians combined Western materials with their own traditions to satisfy multiple markets.

The high-low mix is evident throughout the show, beginning with Dutch Colonial art. One of the earliest pieces on view is an 18th-century depiction of a Dutch farm near Leeds, N.Y., attributed to John Heaten and painted on cherry-wood boards. With its stone house and tiny figures set against the dark scalloped line of the Catskill Mountains, it is among the earliest surviving American landscapes and a very beautiful thing. But far from being a salon piece, it was intended as an architectural ornament to fit over a mantel.

Portraiture steers a course between the expensively overwrought and the cut-rate prosaic. The 1824 likenesses of the New York City businessman John R. Pitkin and his wife, Sophia, have the airbrushed, no-expense-spared perfection of fashion plates. And with their stylish coifs and porcelaneous complexions, they are emblems of the mania for social refinement that swept 19th-century America.

The same obsession lies behind Sheldon Peck's depictions of Elizabeth Ann Ferris Preston of Cato, N.Y., and her husband, but the effect is different. These portraits, too unflattering not to be accurate, have a cookie-cutter format that suggests a rush job. It is as if the sitters, or the artist, were impatient with the task at hand; Mrs. Preston looks cross; Mr. Preston wants to get back to the customers in his general store.

Other portraits are more relaxed. Ammi Phillips's picture of Fanny Waterbury Smith, with her big blue eyes and Nefertiti neck, is a vivacious delight. So is the polychrome wooden head of a young man by the short-lived Asa Ames, and the little watercolor of the Talcott Family -- overworked Mom, bespectacled Dad, Bible-toting mother-in-law -- by the itinerant painter Deborah Goldsmith.

Goldsmith is one of many female artists included in the show, organized by Paul D'Ambrosio, chief curator for the New York State Historical Association. Several were painters. Others concentrated on virtuosic needlework, an example of which is an Edward Gorey-style memorial picture with urns and mourners that looks like a print but is sewn from black silk thread.

And no needlework is finer than that found in a pair of child's moccasins produced by an Iroquois woman around 1800. Woven of porcupine quills and animal sinew, but ornamented with white glass beads and silk ribbons imported from Europe, the shoes are of classic Indian design but may have been intended for a non-Indian recipient.

Later, traditional Indian skills were pressed into service for non-native luxury items, like the beaded velvet pincushions displayed here. And the 19th-century portion of the exhibition concludes with a high-pitched promotional buzz. The final items are garishly colored commercial sculptures, including the figure of a dandyish, aggressively smiling street sharp pushing Battle Ax Plug Tobacco.