A bronze angel by sculptor Augustus Saint Gaudens, valued at more than $100,000, was stolen from Georgetown's Oak Hill Cemetery last Thanksgiving weekend, shortly after a new biography detailed the secret life of the sculptor and his mistress, who modeled for the angel.

A recent statement by Oak Hill's trustees said loss of the statue, known as "Amor Caritas," was kept secret "for nearly three months . . . in hopes the statue would be discovered and quietly returned."

Davida Clark, Saint Gaudens' model and mistress for 25 years, posed for "Amor Caritas," according to "Uncommon Clay," a biography of the sculptor by Burke Wilkinson published last October.

The high-relief sculpture is one of 15 40-by-18-inch versions of the angel cast in a post-1898 edition. Another was sold in 1982 by Hirschl and Adler in New York for $195,000, said Wilkinson.

The original eight-foot-high statue is in the Louvre in Paris. The Corcoran Gallery of Art owns a sister of the Oak Hill statue. The Metropolitan Museum of Art has a larger version.

Wilkinson's biography, recent Saint Gaudens exhibits in Boston and New York and a general revival of interest in 19th-century American art have all combined to boost the value of the 1848-1907 sculptor's works.

The Oak Hill statue was a monument to Joseph E. Willard, first American ambassador to Spain, who died in 1924. Joseph Pozell, superintendent of Oak Hill, said the statue was removed by cutting brass wires fixing it to its pedestal.

The angel, wearing a long robe garlanded with passion flowers, holds a tablet above her head. In his book Wilkinson noted "a good deal of the Renaissance in the graceful figure, much that is Art Nouveau . . . and a romantic lightness and elegance that are Saint Gaudens' very own . . . "

The artist's double life with Davida Clark was concealed for years. Saint Gaudens doesn't mention her in his autobiography. His letters to his mistress were destroyed by Clark's grandson.

Saint Gaudens has many Washington connections, though he lived in New Hampshire. He was a member of the McMillan Commission that prepared the park plan for Washington and drove the stake that marked the location for the Lincoln Memorial. Had he lived, it was understood he would have sculpted the Lincoln figure, finally done by Daniel Chester French.

Saint Gaudens' most famous work locally is the Clover Adams Monument, often called "Grief," in nearby Rock Creek Cemetery. Other works by Saint Gaudens here include "Diana," his only nude, in the National Gallery; several bas-reliefs at the Corcoran; and a Robert Louis Stevenson medallion mounted on the Textile Museum.

Anyone with clues to the disappearance should notify Joseph Pozell at the cemetery at 30th and R streets NW, phone 337-2835.