Nathaniel Benchley, 66, the author of more than a dozen light-hearted, good-humored novels and the son and the father of well-known American writers, died yesterday at New England Deaconess Hospital in Boston.

Mr. Benchley, who lived on Nantucket Island, became ill there about two weeks ago, and after hospitalization on the island, was taken to Boston. He had cancer.

The son of Robert Benchley, the humorist, and the father of Peter Benchley, the author of "Jaws," Mr. Benchley may have been most widely known as the author of "The Off-Islanders," a 1961 novel that was made into the movie "The Russians Are Coming The Russians Are Coming."

Like much of Mr. Benchley's work, the novel conveyed a mood of good-natured fun, in which decent and likable individuals undergo experiences that may be mildly harrowing but that never cause the reader to fear that things will not end happily, as in fact they do.

"Side Street," Mr. Benchley's first novel, drawn from a series of stories of urbanity and urban life he had written for The New Yorker, was also such a book. So, according to reviewers, was his 15th novel, "Sweet Anarchy," published in 1979 and described as full of "zany characterization, eccentric behavior and marvelously sustained nutty dialogue."

Mr. Benchley's characters were constantly bemused and bewildered by the encroachments of modern life on good sense and good nature, but reassuringly, in story after story, they managed to survive and triumph.

Mr. Benchley was born in Newton, Mass., raised in Scarsdale, N.Y., and educated at Phillips Exeter Academy and at Harvard.

His father's occupation, he said, "influenced me as much as anything else. I never seriously considered doing anything but writing." In 1939, the year after college graduation, he became a city reporter on the old New York Herald Tribune. He left to serve in the Navy during World War II, and commanded submarine chasers in both the Atlantic and the Pacific.

After the war he joined Newsweek, but soon gave up his job to become a free-lance writer of both short stories and magazine articles.

In addition to drawing and painting, and watching sports, he once said, his hobby was going to drinking places, "where, I tell myself, I get good ideas for stories," and where he enjoyed the sort of discussions and debates that he styled "saloon dialectics."

In addition to his son, Peter, of Princeton, N.J., he is survived by his wife, Marjorie, of Nantucket, and another son, Nathaniel, of Washington.