At his best, Charles Peale Polk, Washingtonian and early American portrait painter, lights up the walls with strange, attenuated, depthless figures and brilliant highlights, highlights slithering like lightning down the tapestry in back of his subjects -- who included Thomas Jefferson and James Madison.

It's an odd, cartoony, folk-art style congenial with current tastes, not only in its flatness but in its self-consciousness. Polk didn't have to paint this way out of ignorance, he chose to paint this way after a thorough education.

He was the nephew of Charles Wilson Peale, the portraitist, and a cousin to artists Rembrandt, Rubens, Raphaelle, Sarah Miriam and James Peale, a famous and successful family in art. Though Polk's handling of perspective was never too sure, he learned the conventional techniques of the time, the high corner lighting, stately pastoral backgrounds and so on. And then he chose, as his career matured, to abandon them for these erie, almost grotesque pictures, which eventually were lost to everyone but their owners.

"He was completely forgotten," says Linda Simmons, who spent three years rediscovering him for this exhibition, which will be at the Corcoran through Sept. 6. "He was the member of that family who never got his due."

He was also completely American. He was a limner, traveling from town to town in Maryland and Virginia, painting portraits in the style both commercial and artistic of the late 18th and early 19 centuries, painters who spawned a whole genre of art, not quite folk, no quite fine.

"When Europeans see these limners' paintings, they're stunned by them. There's an abstract quality that they like. There's nothing like them in Europe. I think they like them both as artifacts of that period, and for their esthetic values," Simmons says.

There's no apotheosis of the rich and the famous, certainly. His Jefferson -- whom he vastly admired -- does not threaten to ascend bodily into heaven, being, instead, every inch the planter/philosopher, simply dressed, a bit of the mad mechanic about him, abstracted and opinionated, a believer in solutions and human improvement, not terribly forgiving. Physically, on the canvas, he is very there . For all of the increasing strangeness of Polk's portraits, and for all of their cartoony flatness, they have a quality of realness and ordinariness that seems wonderfully American too.

"We don't know how Polk thought about art becase he never mentions it in his letters, so his tyle is a mystery," Simmons says. "All we know is that his uncle never criticized his work, which may mean that he was pleased with it. He never held back from criticizing his children."

He was born in Annapolis in 1767, son of a seafarer and privateer. He moved to Philadelphia in 1775, where he became absorbed into his uncle's family and trade. He later lived in Baltimore and Frederick, operating a dry goods store and putting out a ship for charter, along with his travels with his easel. Money problems dogged him always -- he decalred bankruptcy in 1804 and 1812. In 1802 he moved to Georgetown, writing to his hero and portrait subject, President Jefferson, for a job to support his "Dear Suffering family who, at this time want the necessaries of Life."

Jefferson sent him $25, a large sum, back then. Later that year, he asked for a job as a clerk in the Treasury, and during the next 20 years painted only occasionally. (his lifetime output was probably around 500 pices.) He moved to Richmond County, Virginia, in 1820 to live on some land his third wife had inherited, and when he died in 1822, neither of his two obituaries mentioned that he had been an artist.

He was clearly of an extravagant temper. His self-portrait, which lacks many of the odd mannerisms of his other work, shows a darkly intense man with a stubborn set to his face. He was twice excommunicated from the First Baptist Church in Washington -- of which he was founder -- for being, in the first instance "a general Disturber of our Peace," and late for bankruptcy, and not attending.

The paintings are nicely hung at the Corcoran in an 18th-century setting including dentilated woodwork, trompe l'oeil chair rails, and a demilunette card table.

The show should heighten the growing interest in early American painting, and it's an intimate look at an American citizen artist, before all the trappings of romanticism came in.