Because he shocked the critics, overthrew convention, and plunged into the new, Alfred H. Maurer - "America's first modern painter" - has often been described as a pioneer and a hero.

There is no doubt that Maurer picked a winning side. He early on allied himself with Steichen and the Steins, with the new Parisian painting, with the Cubists and the Fauves - but though his daring earned him strong modernist credentials it did not help his art.

Maurer (1868-1932) left New York for Paris in 1897. It was there, in 1905 or 1906, that he saw the light. It would be pleasing to report he had discovered a new beauty, but it seems, at least to me, that the pictures he produced after his conversion grew uglier and uglier.

The Hirshhorn Museum and Sculpture Garden owns, and is now showing for the first time, 17 Alfred Maurers. His little exhibition, which begins with charming portraits done before his "breakthrough," has a dismal ending. It is rare to see in a museum portraits as embarrassing, as laughable and clunky, as the late works by Maurer that are here on view.

Look, for instance, at his "Claudia (Woman Before the Mountain)," circa 1929. Her lip curls and her eyes bulge, her nose is much too long. Beautiful she is not.

The fashionable paintings of fashionable women that Alfred Maurer made before his conversion have none of her suspect primitivism, her forced naivete. Languorously, gracefully, they pose, in muted grays and browns, in long skirts and big hats. Their parentage is obvious. They take their coloring from Whistler, and their bravura brushwork from John Singer Sargent. One such Maurer portrait, Whistleresque in coloring and in title - it was called "The Arrangement" - won for Alfred Maurer a gold medal and a $1,500 prize at the Carnegie International exhibition of 1901. He was rarely to achieve such success again.

Through he was 5-foot-2, Maurer, on the Left Bank, cut a dashing figure. He wore a cape, a broad-brimmed hat; he affected spats, a cane. He enjoyed the dancing at the Moulin Rouge (as did Monet, Toulouse Lautrec, Renoir and Degas); he lived La Vie Boheme; he hung out with the Steins. But when he returned to New York at the start of World War 1, his life began to slide.

Some still blame his father, Louis Maurer, an opinionated and unforgiving man. Was Maurer, while in Paris, rebelling against the art conventions of the Brown Decades, or against his father? It is difficult to tell.

Louis Maurer, German-born, moved to the United States when he was 19. A lithographer by training, he often designed prints for Currier & Ives. He had left school for the print shop when he was 16. He made his son do the same.

It is said that when the father saw his son's first New York show (at Edward Steichen's "291" gallery in 1909) he was so distressed, he wept.

The critics, too, were bothered by young Maurer's wild brushwork and just-as-wild colors. "What is Maurer after?" asked James Gibbons Huneker. "A Catherine Wheel at full tilt on a 4th-of-July night, or an ordinary apoplectic aura?" Arthur Hober, the president of the National Academy, was even more offended. "Of all the pure forms of imbecility that have overtaken youth time out of mind, these are the limit," he opined. Such pans are often quoted by minions of modernism to make the reader smile at the blind fulminations of those conservative old fogies, but those who see the modern Maurers hanging at the Hirshhorn may leave the show believing that Hober had a point.

Returning a Manhattan, Maurer took a little third-floor bedroom in his family's house on 43rd Street. It was in that room he died.

In 1925, the scores of modern paintings that the young Maurer had left behind in his Paris studio were sold off for back rent. In 1929, the father, not the son, suddenly became an art celebrity in New York.

It was that year Harry T. Peters published his "Currier & Ives: Printmakers to the American People." The book praised Louis Maurer, the last Currier & Ives printmakers alive. When in 1931, at the age of 99, Louis Maurer was given his first one-man New York show, the reporters came in droves. "The son is also an artist," their feature stories noted.

Louis Maurer was 100 when he died on July 19, 1932. Alfred Maurer, free at last at 64, hanged himself two weeks later.

Maurer was no coward. His Cubist pictures do not look like those of the French Cubists, and his later women, ugly as they are, are not unoriginal. But he was no master. He gave himself to modern art and was in the right place at just the right time, and he thereby earned himself a place in the art texts and museums. But his devotion to the new - or his hostility to the old - did not improve his art.

Joseph H. Hirshhorn's Maurer collection is a bit lopsided. Early and late Maurers are both well represented, but the telling transitional pictures of 1906 through 1914 are missing from this show. It was organized by Judith Zilczer, the museum's historian. It closes Aug. 12. CAPTION: Illustration, Detail from "Claudia" ("Woman Before the Mountain")