Her death was confirmed by family members, which said she suffered a stroke last week and had been hospitalized since.

Mrs. Konigsburg was the only author to have won the American Library Association's John Newbery Medal for distinguished children's literature, considered the most prestigious in the field, and been the runner-up in the same year.

She received the 1968 medal for "From the Mixed-Up Files of Mrs. Basil E. Frankweiler," a story about a sister and brother from the suburbs who run away from home and surreptitiously camp out at the Metropolitan Museum of Art in Manhattan. She wrote that book in 1967, the same year she finished and sold her first book, "Jennifer, Hecate, Macbeth, William McKinley, and Me, Elizabeth," about a new child in the neighborhood and her friendship with a girl who claims to be a witch, the 1968 Newbery runner-up.

Ingrid Bergman played the role of Mrs. Frankweiler in a 1973 film version of the book, which was also made into a television movie in 1995, with Lauren Bacall in the same role.

Mrs. Konigsburg won the Newbery again in 1997 for "The View From Saturday," about four members of a sixth-grade interscholastic quiz bowl team and the paraplegic teacher who coaches them.

Mrs. Konigsburg's 20 books, about half of which she illustrated herself, are known for their outsider's perspective, their wit, and plotlines that venture fearlessly into unfamiliar epochs, fantastic scenarios and nightmarish circumstances that might have been plucked from the headlines.

In her 1986 novel, "Up From Jericho Tel," an actress gives two children the power of invisibility to send them on a quest. "A Proud Taste for Scarlet and Miniver" (1973) is a historical fantasy about the life of Eleanor of Aquitaine as told by her and her contemporaries, all now living in heaven. "Father's Arcane Daughter" (1976) recounts what happens when a girl who was kidnapped and presumed dead 17 years ago reappears to find her mother long dead and her father remarried, raising a new brood. In "Silent to the Bone" (2000), one of her darkest plots, a 13-year-old boy is wrongly accused of seriously injuring his baby sister - and the accusation, coupled with his sister's injury, renders him mute.

Acts of kindness and flashes of insight resolve most of her characters' troubles; serendipity takes care of the rest.

Roger Sutton, reviewing "Silent to the Bone" in The New York Times, described Mrs. Konigsburg as "one of our brainiest writers for young people, not only in the considerable cerebral powers she brings to her books but in the intellectual demands she makes on her characters."

Elaine Lobl was born Feb. 10, 1930, in Manhattan, the second of the three children of Beulah and Adolph Lobl. She later described her parents as modest, hard-working people who never imagined their children would go to college and could not afford it if they had.

After graduating at the top of her high school class in Farrell, Pa., where her family had moved, she held various jobs, hoping to save toward her eventual college studies, including one as a bookkeeper in a local meatpacking plant, where she met David Konigsburg, a brother of the owner.

By the time they were married in 1952, Mrs. Konigsburg had graduated from the Carnegie Institute of Technology in Pittsburgh with a major in chemistry. When her husband finished his doctoral studies in psychology at the University of Pittsburgh, they moved to Jacksonville, Fla., and started their family. She began writing when her children went to school.

Mrs. Konigsburg is survived by her three children, Paul, Laurie and Ross, and five grandchildren. Mr. Konigsburg, an industrial psychologist, died in 2001. In interviews, Mrs. Konigsburg said her upbringing in small-town Pennsylvania, where she did not have great expectations, helped her as a writer.

"Growing up in a small town," she told a biographer, Renee Ambrosek, in 2006, "gives you two things: a sense of place and a feeling of self-consciousness - self-consciousness about one's education and exposure, both of which tend to be limited. On the other hand, limited possibilities also mean creating your own options."

In a separate interview, she said: "I think most of us are outsiders. And I think that's good because it makes you question things."