Marian King, 86, a lifelong Washington resident and the author of 29 children's books and historical novels, died of a stroke March 12 at her home in Washington.

Miss King wrote her first book, "The ABC Game Book," in 1928. Her last book, "Adventures in Art," a commentary on children's paintings in the National Gallery of Art, was published in 1978. Although most of her work was for youngsters, her historical novels, such as "Elizabeth, the Tudor Princess," which appeared in 1940, also appealed to adults.

Miss King was born in Washington, where her family owned the old King's Palace department store. She graduated from the Madeira School in the Greenwood section of McLean.

As a child, Miss King was interested in sports, and she learned to play tennis from an uncle, Philip King, who had played football at Princeton. In time she became a notable tournament tennis player.

Tennis also led to her first book. "I was playing in a tennis tournament, an indoor tournament, and the Davis Cup captain was on the sideline," she told William R. MacKaye of The Washington Post in an interview in 1979. "I was standing next to him, and he said, 'Oh, Marian, let's do a book.' And I said, 'Yes, let's do it.' "

Miss King said she had a title and an outline for her book by the next day, but that her friend never got started at all.

In his profile of Miss King in The Post, MacKaye said, "She betrays the same perturbed, faintly worried, almost obsessive preoccupation with words that is the writer's blessing and curse. Indeed, writing finally drove her away from her second love, playing tournament tennis."

Miss King, who retired in 1981, traveled extensively in Europe and elsewhere to gather original material for such books as "Kees and Kleintje," published in 1930, a story about a Dutch boy and his pet duck, and "It Happened in England," published in 1939, about two English children living on a farm.

In addition to her books, she wrote short stories and articles that appeared in such publications as The Washington Post, The Christian Science Monitor, Saturday Review, and Highlights, a magazine for children.

Miss King was a member of the Children's Book Guild and The Hospitality Information Service.

Survivors include a sister, Hilda Sommers of Washington.