Mr. Adams readily acknowledged criticisms that “Watership Down” borrowed much rabbit lore from R. M. Lockley’s nonfiction study “The Private Life of the Rabbit” (1964). But the authenticity of Mr. Adams’s book as an anthropomorphic fantasy with classic motifs was not challenged, and in Britain it won the Carnegie Medal in Literature in 1972 and the Guardian Children’s Fiction Prize in 1973.

In 1974, Macmillan published the first United States edition. American reviews were mixed.

Peter Prescott gave it a glowing review in Newsweek. Alison Lurie, in The New York Review of Books, called it “a relief to read of characters who have honor and dignity, who will risk their lives for others.”

But Richard Gilman, in The New York Times Book Review, said it fell far short of Lewis Carroll’s “Alice in Wonderland” and Kenneth Grahame’s “The Wind in the Willows,” and predicted it would “find its true audience mainly among the people who have made a cult of Tolkien, among ecology-minded romantics and all those in need of a positive statement, not too subtle but not too blatant either, about the future of courage, native simplicity, the life-force, and so on.”

”Watership Down” struck it rich. It quickly topped the New York Times best-seller list and remained on it for eight months. It was a Book of the Month Club selection. Avon paid $800,000 for the paperback rights. It eventually became Penguin’s all-time best seller, a staple of high school English classes and one of the best-selling books of the century, with an estimated 50 million copies in print in 18 languages worldwide.

Mr. Adams quit the civil service in 1974 to become a full-time writer. He published a score of books: novels, short stories, poetry, nonfiction and an autobiography. Some sold well, but none approached the success of “Watership Down,” which was adapted for a 1978 animated film (with a song, “Bright Eyes,” sung by Art Garfunkel), an animated television series broadcast in Britain and Canada from 1999 to 2001, and a theatrical production in London in 2006.

Mr. Adams was a stout, ruddy-faced man with a big chin and a flying shock of silver hair that complemented his Harris tweeds and country life. He wrote longhand with a pen or pencil, producing 1,000 words a day. Before each session, he read aloud from Milton’s “Paradise Lost,” Spenser’s “The Faerie Queene” or C. K. Scott Moncrieff’s translation of Proust.