After working for the State Department in Washington, Ms. Sifton began her literary career in 1962 with Frederick A. Praeger Publishers. In 1968, after the company was sold, she joined the Viking Press as an editor; she was named editor in chief in 1980. She was executive vice president of Alfred A. Knopf from 1987 to 1992 and then joined Farrar, Straus & Giroux as senior vice president and publisher and editor at large of its subsidiary Hill & Wang.

She retired from editing full time in 2008.

In the late 1980s Ms. Sifton was among the first 20 women admitted for membership in the Century Association, the venerable New York private club, after it lost its legal challenge to a city human rights law that prohibited discrimination on the basis of gender.

In 1998 she began exploring the derivation of the Serenity Prayer, which had been widely attributed to Niebuhr and popularized by Alcoholics Anonymous and other 12-step programs.

She remembered the prayer from 1943, when her father preached from the Union Church in Heath, Mass., a farming village in the northwestern part of the state where the family spent summer vacations. Other sources quoted Niebuhr from a decade earlier, and he himself later wrote that the prayer “may have been spooking around for years, even centuries, but I don’t think so.”

“I honestly do believe that I wrote it myself,” he said.

The prayer has appeared in various forms, though, including: “God, give us grace to accept with serenity the things that cannot be changed, courage to change the things that should be changed, and the wisdom to distinguish the one from the other.”

Ms. Sifton later reflected on the prayer. In one interview, she said: “Every single day one has to think, Is this something that I should accept with serenity, or is this something I should try to change? That’s the deep conundrum that serious people think about all the time.”

As an editor, Ms. Sifton “had read deeply enough in literature and history that she could immediately see what was fresh, or why the question investigated or thesis proposed was urgent and necessary,” Dan Frank, the editorial director of Pantheon, said in an email.