UNCOMMON CLAY: The Life and Works of Augustus Saint Gaudens. By Burke Wilkinson. Photographs by David Finn. Harcourt Brace Jovanovich. 428 pp. $22.95.

AUGUSTUS ST. GAUDENS (1848-1907) was a robust, athletic figure with strong legs and deft hands who loved to swim and ride horses. He was a great talker, a tireless workman who sang in his shop, always loudly and off-key. He was also a gifted artist, the first American sculptor to win international acclaim.

St. Gaudens' monuments reach across this nation, from Boston Common to a mountain top in southern Wyoming. His works celebrate great victors (Lincoln, Sherman, Farragut) but also brood upon defeat (the shrouded, nameless figure at the Adams grave in Washington's Rock Creek Cemetery). St. Gaudens had no formula for his art, only energy and curiosity: "You have often wondered," he wrote to a niece, "what I think about things. I wonder myself. I think anything and everything."

Burke Wilkinson's biography has a similar inclination, to view its subject with generous enthusiasm rather than cool appraisal. In this life, St. Gaudens is the force who organized American artists and led them to wealth and respectability. He helps to design U.S. coinage, the Chicago World's Fair of 1893, and the Capitol Mall in Washington. He moves and shakes the trans-Atlantic art scene with a bullish vigor, matching "his bold, tawny look of a Renaissance soldier of fortune."

Military images dominate Wilkinson's narrative, which is long on scenes of conflict and strategy, sketchy on analysis of character. We learn much about politics, business contracts, and sculpting methods, but less about St. Gaudens' wayward, moody temper -- or the many masks he wore throughout his career.

But Wilkinson certainly tells a richer story than St. Gaudens' own memoirs, written on his deathbed and later censored by his wife and children. The principal omission: his secret life with Davida Clark, a Swedish model who bore him a son and whom he maintained in a separate domicile for nearly 30 years. She was always nearby, whether St. Gaudens worked in New York, Paris, or his atelier in New Hampshire.

Facts about Davida are scarce, but Wilkinson has uncovered some suggestive shards. The name "Davida" was St. Gaudens' creation, to honor Michelangelo's David -- and probably her classical looks. She had a strong yet sensuous beauty, qualities that inspired his Amazon figures -- Diana, Victory, the Amor Caritas. In the sculptor's hands Davida became a divinity, soaring beyond her simple self. His letters to her are gone; hers to him were "poorly written and illiterate."

The longsuffering role in this drama was played by St. Gaudens' wife, Augusta. Handsome and artistic in her youth, she faded during marriage into a tiresome "worry bones," ever fretful about finances and her state of health. She was pitifully deaf, isolated from laughter and conversation by the roaring in her head. But her sharp eyes spied Davida, and bitter scenes ensued. The marriage went on, sustained by habit and a stubborn loyalty to memories. After St. Gaudens' death, Augusta devoted herself to keeping his fame alive.

WILKINSON tells this story with just and sensitive touches, but he never quite determines its place in the artist's psyche. The infidelity was no casual affair, but a case of deeply conflicting loyalties. Born of immigrant parents, St. Gaudens rose from his working-class background to marry a woman of superior status. Success brought him fame and wealth, the patronage of Morgans and Vanderbilts -- and he fell in love with a young, poor, immigrant girl. That she strongly resembled his mother seems to complete the compensatory cycle. Having reached a peak, he tried to recover all that the climb had cost him.

A similar nostalgia apparently governed St. Gaudens' career. He began as an apprentice craftsman, carving portrait cameos in ivory, and gradually rose through Beaux Arts training to become a sculptor. Something in him distrusted this large-scale modeling. He rarely refused commissions, delegating them to assistants and then slowing their progress by calling for endless revisions. Yet on his own he swiftly turned out brilliant low-relief portraits, silhouettes in clay that recall his early cameos.

In the masterworks he managed to please himself, if not others. Henry Adams proved to be the kindest patron, freeing St. Gaudens to create an image of human repose -- the exact opposite of Adams, whom St. Gaudens later caricatured as a winged porcupine. The Shaw memorial was another story, a 15-year battle with sponsors to win the final scene: Robert Gould Shaw marching with his doomed black soldiers, and above them an angel, the spirit that hovers beyond war and race.

Wilkinson selects the Sherman monument as St. Gaudens' supreme effort, though he notes that this version of warrior and angel had many sharp critics. One was Henry James, who suspected "all attempts, however glittering and golden, to confound destroyers with benefactors."

A shrewd biographer, Wilkinson never errs in that direction. His life of St. Gaudens is an absorbing and accurate story, which may well live to confound the sculptor's prophecy: "A poor picture goes into the garret, books are forgotten, but the bronze remains."