Helen MacInnes, 77, a gifted and prolific storyteller whose 21 novels of suspense, espionage and intrigue established her as one of the world's foremost writers of international spy fiction, died Sept. 30 in a New York hospital three weeks after having a stroke.

"Take away the sense of adventure from man, and you have plab," Miss MacInnes once said.

In a career that spanned more than four decades, her imaginary heroes and heroines battled Nazis during the 1940s and communists thereafter, and their adventures were followed faithfully by a global network of mystery buffs who purchased 23 million copies of her books in 22 languages.

Four of her novels were made into movies, including her first, "Above Suspicion," published in 1941. Her most recent novel, "Ride a Pale Horse," is currently a paperback best seller.

Miss MacInnes was said by critics to have had few equals in the mystery writer's art of unraveling the details of stories bit by bit, quickly enough to keep readers' interest, but not so fast as to tip a hand too soon.

She usually followed a basic and time-honored stratagem: an ordinary person, possibly an architect, lawyer or historian, is suddenly swept up in a vortex of international espionage and skulduggery by dint of some commonplace action, picking up a wrong raincoat at an airport, for example.

Allen Dulles, former head of the CIA, said Miss MacInnes was a "natural master of the thriller," and he included a selection from her second book, "Assignment in Brittany," in his anthology, "Great Spy Stories From Fiction."

Known for a highly literate style, Miss MacInnes found the ideas for many of her stories in her travels and in real-life events. Her encounters with Nazis during her honeymoon in Bavaria during the 1930s provided much of the material for "Above Suspicion," for example. A newspaper account of a diving operation in a Czechoslovakian lake to recover boxes sunk by the retreating Nazis became the inspiration for "The Salzburg Connection," which was published in 1969 and also was made into a movie.

She was on vacation in Greece when she got the idea that led to "Decision at Delphi," a 1960 best seller. "I don't pick the settings for my books. The places seem to pick me," she said. "They tap me on the shoulder and say, 'Hey! Helen.' "

She was a diligent researcher who made the settings for her stories come alive with authentic background details, and she was widely acknowledged to be perceptive in her handling of political issues.

"I'm a research historian," she once said. "I went to the trial of Col. Rudolf Abel the Soviet spy exchanged for Francis Gary Powers in 1962 to study the eyes, expressions. I want hard facts, want to know what I am writing about."

Born in Glasgow, Miss MacInnes met her husband, Gilbert Highet, while at the University of Glasgow, and she came to the United States with him in 1937 when he accepted an appointment to the classics faculty at Columbia University. He died in 1978.

As the young bride of an Oxford don, she had thought of writing a novel even before coming to the United States, and one night in New York in 1939 as their infant son was hospitalized with a ruptured appendix, Highet picked up a pad of notes and commentary Miss MacInnes had been keeping on contemporary politics and the rise of Hitler.

"Helen, dear, I think you are now ready to write your novel," she recalled him saying after he had read her notes.

"So he gave me a yellow pad and two sharpened pencils. That's how it began. I got myself a clipboard and said, 'I'm going to tell myself a story.'

"Above Suspicion" was followed in short order by "Assignment in Brittany," a tale of World War II espionage that also became a movie, and there followed a novel every two or three years.

Among Miss MacInnes' other well-known novels are "The Venetian Affair," which was also made into a movie, "The Snare of the Hunter," "Double Image" and "Message from Malaga."

She is survived by a son, Keith, of Englewood, N.J.