Douglass Wallop III, 64, a native Washingtonian whose best-selling 1954 novel, "The Year the Yankees Lost the Pennant," became the popular Broadway musical and later the movie, "Damn Yankees," died April 2 at Georgetown University Hospital. He had a heart ailment.

Mr. Wallop was a frustrated Washington Senators fan, as was the hero of his novel, a middle-aged Washington real estate salesman named Joe Boyd who lived out the Faustian fantasies of thousands of other pennant-starved Washington baseball fans. He made a pact with the devil to become transformed into young Joe Hardy, a baseball superstar who led the Senators to the American League pennant.

It was Mr. Wallop's second novel, and it was an instant success. It was a Book-of-the-Month Club selection, and a Readers Digest Condensed Book Club selection, and it sold more than 2.5 million copies. The following year the Broadway musical "Damn Yankees" opened, and in 1958 it was made into a movie starring Gwen Verdon and Tab Hunter.

For Mr. Wallop, it meant financial independence that enabled him to devote full time to his writing career, and he wrote a dozen more novels over the next three decades, although none achieved the popular or financial success of "The Year the Yankees Lost the Pennant." A 1969 novel, "The Good Life," about life among the rich on Maryland's Eastern Shore, where Mr. Wallop had lived since 1963, was adapted for a television serial starring Larry Hagman during the early 1970s.

Mr. Wallop was raised in Washington, graduated from the old Central High School and the University of Maryland and worked as an overnight rewrite man for United Press in Washington during World War II. Later he wrote for the Associated Press and NBC radio in New York, and in 1948, while working temporarily as a desk clerk at a hotel in Ocean City, snapped up an offer from Doubleday & Co. to take dictation from Gen. Dwight D. Eisenhower for Eisenhower's book, "Crusade in Europe."

Like many journalists, Mr. Wallop had long dreamed of being a novelist, and in the early 1950s he decided to give it a try. He took a job selling insurance at his father's insurance agency in Washington during the day, and he spent his nights writing. In 1953 his first novel, "Night Light," was published, but it was only minimally successful. It was a story about a father's struggle to find an explanation for the murder of his daughter by a maniac.

Then, in September 1953, Mr. Wallop put aside the rough draft of second serious novel he was working on to work on a baseball fantasy that had been in the back of his mind all summer. It took him just over three months to write "The Year the Yankees Lost the Pennant," and the novel was published the following spring.

In Mr. Wallop's version of the Faustian legend, the hero of his novel insists on an escape clause in his pact with the devil. He resists a variety of temptations and invokes the escape clause at the last minute, just in time to avoid perdition, but the Senators still win the pennant by beating the Yankees on the last day of the season.

The Senators' last pennant before publication of "The Year the Yankees Lost the Pennant" was in 1933, and it was only in the fantasy of Mr. Wallop's novel that they won one after that year. The team left Washington for good after the 1971 season.

An avid sports fan, Mr. Wallop also wrote a book about professional football, "This is What Happened to Charlie Moe," published in 1965. He wrote "Baseball, An Informal History," in 1969 on the 100th anniversary of the invention of the sport.

His books ran the gamut from serious dramas to lighthearted ironies. Mr. Wallop's last novel, "The Other Side of The River," was published two years ago. Set partially on the Eastern Shore, it was a story of a man's quest for revenge after his wife leaves him for another man, and then commits suicide.

A resident of Oxford, Md., Mr. Wallop was an enthusiastic tennis player and sailor and had also written a book about the Oxford Regatta.

He is survived by his wife, Lucille Fletcher Wallop, also a writer, of Oxford; two stepdaughters, Dorothy Louise Silverman of New York City and Wendy Elizabeth Harlow of Baltimore; two brothers, Dr. William Holland Wallop of Annapolis and Dr. Edgar Ellis Wallop of Kent Island, Md., and two grandchildren.