Frank Mankiewicz, a writer and Democratic political strategist who was Senator Robert F. Kennedy’s press secretary, directed Senator George S. McGovern’s losing 1972 presidential campaign and for six years was the president of National Public Radio, died on Thursday in Washington. He was 90.

The cause was heart failure, said Adam Clymer, a family spokesman, who is a former reporter for The New York Times. Mr. Mankiewicz, who lived in Washington, died in a hospital, where he had been treated for heart and lung problems, Mr. Clymer said.

A scion of Hollywood, the son of Herman J. Mankiewicz, who wrote “Citizen Kane,” and the nephew of Joseph L. Mankiewicz, who directed “All About Eve,” Mr. Mankiewicz grew up with an Algonquin West round table in his Beverly Hills home, regaled by movie stars and famous writers.

He became a journalist and lawyer and, inspired by the Kennedys, went to Washington at the dawn of the New Frontier and took an executive position at the Peace Corps, full of idealistic hopes. What he encountered were assassinations, the Vietnam War and the Watergate scandals.