A white marble figure of Harriet Newcomer, once owner of Scaleby, a country estate in Boyce, Va., sold for $50,000 Tuesday to Jo Ann and Julian Ganz Jr. of Los Angeles, Calif., in a Christie's onsite auction.

The figure, sculpted in Rome in 1868 by William Henry Rinehart, will be displayed from Oct. 4 to next Jan. 31 in the National Gallery of Art's "An American Perspective, 19th Century Art From the Collection of Jo Ann and Julian Ganz Jr."

Harriet Newcomer, later Mrs. Henry B. Gilpin (1861-1942), is shown as a small girl in the 75-inch statue, carved in the neoclassic manner, the folds of the dress so real you expect them to move. Harriet Newcomer Gilpin was a daughter of Benjamin F. Newcomer, founder of the Atlantic Coastline Railroad, and mother of the late Kenneth N. Gilpin, whose estate was auctioned.

The figure brought the highest price in the two-day sale, which ended yesterday, knocking down $490,683, near the highest estimate for all 700 lots of furniture, silver, Oriental porcelain, bronze sculpture, antique weapons, linen and lace, books, prints, paintings and rugs. Virginia furniture, iron garden furniture, silver and Chinese Export china all sold at the high estimates.

Other important prices: A Federal inlaid cherrywood desk and secretary, made in Virginia around 1800, brought $21,000; a late Federal mahogany three-pedestal base dining table, made in New York about 1810-20, brought $15,000; and a set of approximately 25 pieces of Chinese Export Armorial china, circa 1765, probably made for the Portugese market, sold for $14,000. Glenn Randall, an Alexandria antique dealer, bought the table and the china. gThe other buyers' names were not given.

Scaleby, named for the Gilpin family's English country seat, was built in the classic revival style around 1909, to the design of Howard Sill, a Baltimore architect. Fourteen gardeners once maintained the acres of formal gardens. The original owner, Henry B. Gilpin, bred horses. His son Kenneth was president of Fasig-Tipton, a company that auctioned yearlings.

An oil painting of a "White Horse in a Wooded Landscape" by Sawrey Gilpin, an ancestor of the Virginia Gilpins, sold for $80,000 in New York in May at Christie's. The painting had hung at Scaleby.