"To say I'm astonished is an understatement," said the 67-year-old Sontag, who didn't pretend not to enjoy the award. "I'm really more moved than I could say."
Oscar winners like to joke that they rarely win for their best work; many would say the same about In America, the novel that brought Sontag her first National Book Award on Wednesday night.
Based on the life of the 19th century stage performer Helena Modjeska, In America was Sontag's first novel since the acclaimed 1992 best seller The Volcano Lover. Although highly anticipated, the new book spent little time on best-seller lists and received a number of negative reviews. The New York Times' Michiko Kakutani labeled it "a banal, flat-footed narrative."
Sontag, author of such influential nonfiction works as Against Interpretation and Illness as Metaphor, was also criticized for the uncredited borrowing of passages from other sources.
But novelist Ron Hansen, chair of the National Book Award fiction committee, praised In America as the "heart and majesty" of American writing in 2000. In a post-ceremony press conference, Sontag said she was too "squeamish" to read reviews and questioned their value.
"I often feel that I really know better what's wrong than any reviewer does," she said.
Other fiction finalists included Joyce Carol Oates' Blonde, based on the life of Marilyn Monroe; Francine Prose's Blue Angel and Charles Baxter's The Feast of Love. Alan Lightman was nominated for The Diagnosis.
Also Wednesday, the nonfiction award went to Nathaniel Philbrick for In the Heart of the Sea, the story of the whaling ship tragedy that inspired Herman Melville's Moby Dick. Runners-up included 92-year-old Jacques Barzun, author of the 800-page best seller From Dawn to Decadence, and Patrick Tierney, author of the much-debated anthropological investigation Darkness in El Dorado.
The poetry prize went to Lucille Clifton for the compilation Blessing the Boats, and the young people's literature award went to Gloria Whelan for Homeless Bird, the story of a girl in India who is married and widowed at age 13.
Ray Bradbury, best known for the futuristic novel Fahrenheit 451 and the science fiction classic The Martian Chronicles, received an honorary medal.
The awards are sponsored by the National Book Foundation, a nonprofit organization. Winners receive $10,000 each and other finalists $1,000 each.