EVEN WHEN life is long, art is longer. Worthington Whittredge painted for more than 60 of his 90 years, and seems to have learned something every day. Yet it's clear from a marvelous exhibition at the Corcoran that his muse was leading Whittredge on just as merry a chase at the end as in the beginning.

Ohio-born and largely self-taught, Whittredge (1820-1910) is assigned to the Hudson River School, as is just about every 19th-century American who painted lots of large, bright landscapes.

But Whittredge doesn't categorize that simply. After polishing his painting skills in the East, he spent a decade in Europe, where he produced scads of fussily composed, highly sentimental and quite appealing rural scenes. Back in America, he experimented with many styles, producing some jewels in the Barbizon manner. His later works suggest that if he'd been younger he'd have wholeheartedly embraced impressionism.

During his European sojourn Whittredge was based in Duesseldorf, where he occasionally overdosed on gemuetlichkeit and committed such kitsch as "Happy as a King" (1843), in which four bucolic cherubs gambol on and around a gate. In the background, where one would expect to see a bosky dell, is a forest as brooding and Teutonic as the one in which Hansel and Gretel so nearly came to grief. The painting is a shameless attempt to cloud our minds and win our hearts, and it works.

So do nearly all of Whittredge's European scenes, most of which tell stories of hunt or harvest. In the most successful ones, such as "Landscape Near Minden" (1855), the story is a subplot, with small figures placed off the main axes created by trees and landforms. But the real subject is light, lots of light, so much of it that instead of shadow he sometimes just uses a little less light.

Whittredge came home to discover that his contemporaries had learned even more about light than he had, but soon got up to speed and outraced all except Frederic Edwin Church. He and Whittredge poured such fire over their canvases they all but burned out the Hudson River School. Perhaps because he knew he was not Church's equal as a pyrotechnician, Whittredge continued to use storytelling to direct the viewer. In "Twilight on the Shawangunk Mountains" (1865), the foreground is subtly busy with hunters, whose activities engage the mind long enough to let the background sunset saturate the eye.

Whittredge made two long journeys to the American West in the 1860s and '70s, but the wide open spaces overwhelmed him. In the East, as in much of Europe, the landscape comes pre-framed with foliage or landforms, and the horizon is near at hand. The Big Skycountry seems to have made Whittredge nervous, and though he tried some scenes repeatedly, he never managed to quite bring them off.

Depicting the same stretch of the Cache La Poudre River twice in 1863, and a ford on the Platte River in 1866 and 1868, Whittredge fumbles with the focus and the framing; when he emphasizes the foreground, the background dominates, and when he tries to bring up the background the foreground intrudes. And his color perception, developed amid Eastern and European greenery, doesn't seem to have been able to register the thousand shades of gray that dominate the Western landscape, particularly the plains he mainly painted.

Happily, each time Whittredge returned from the West he saw familiar Eastern scenes afresh, and the result was such delicious, intimate vignettes as "The Woods of Ashokan" and "The Trout Pool" (both 1868). No one has better rendered the play of sunlight on and in the water of a woodland stream, and how, at certain hours, the forest seems lighted from below. It's cruel hard to leave such canvases and go out upon city streets.

Longevity made Whittredge dean of the Hudson River School, which he proceeded to close down. "A Breezy Day, Sakonnet Point, Rhode Island" (1880) is all cool light and muted life and, while clearly influenced by the Barbizon School, is not at all French. It's as though, having painted with a torch for so long, Whittredge decided to try a candle. "Noon in the Orchard" (1900), among his last major works, owes much to impressionism but seems to be essentially the 80-year-old artist's attempt to rediscover shadow. It's a handsome coda to a long life spent making the utmost of a very large talent that wasn't quite genius.

WORTHINGTON WHITTREDGE, HUDSON RIVER ARTIST -- Through Nov. 4 at the Corcoran Gallery of Art, 17th Street and New York Avenue NW. 638-3211. Open 10 to 4:30 Tuesday through Sunday and 10 to 9 Thursdays. Call ahead for wheelchair access.