Thomas Sully (1783-1872) was America's finest portraitist, a shameless flatterer, a genius or a hack, according to various critics.

He was all of the above, according to Monroe Fabian, a National Portrait Gallery curator who has assembled 81 of Sully's paintings and drawings in a show designed to support all points of view.

It's the first major Sully exhibition in more than 60 years, and Fabian had a devil of a time making his selections from among the artist's more than 2,000 works executed over a span of seven decades. He also had a heck of a time prying some of them loose from their owners: Many Sullys have been treasured and fought over through many generations of leading American families; others, one suspects after viewing the show, have been hidden in closets by persons of taste.

The paintings are grouped more or less chronologically, which shows that Sully, as Fabian says, "didn't have good periods or bad periods so much as good days and bad days." Two portraits of actors, both done in 1811, illustrate the statement perfectly: "George Frederick Cooke in the Role of Richard III" is a delight; "William Burke Wood in the Role of Charles de Moor" is a disaster.

It can be said that Sully did most of his best work in his first 20 years, then slid for half a century on his reputation. Yet again and again, he produced outstanding later works such as his 1848 portrait of his wife with their dog and an 1864 portrait of Edward James Roye, fifth president of Liberia. The portrait of Sarah Sully was done for their daughter Blanche and, as the catalogue says, "is exquisite proof that at age 65 Thomas Sully could still produce a first-rate portrait when he did not have to acquiesce to the demands of fashion or a client." The Roye portrait, done from a photograph in Sully's 81st year, is all the more remarkable a piece of work because it's one of only two the artist ever attempted of black subjects.

The catalogue, available at the gift shop, is an absolute necessity. Fabian's scholarship is unremitting and unblinking, and has benefitted enormously from the detailed journals and studio records Sully kept. It amounts to both a good read and a major biography of the artist. MR. SULLY, PORTRAIT PAINTER -- Through September 5 at the National Portrait Gallery (Gallery Place Station on Metro's Red and Yellow lines). Open 10 to 5:30.