Some version of this occurs almost everywhere Caroline Kennedy goes.

A perfectly well-intentioned person she has never met approaches her to say that a relative is entering politics because of her father, John F. Kennedy. Or expresses sympathy for the loss of her brother, John F. Kennedy Jr., who was killed in a plane crash in 1999, or her mother, Jacqueline Kennedy Onassis, who died from lymphoma in 1994.

These interactions happen on the subway (the main way she gets around New York). They happen on Martha's Vineyard (where she spends her summers). They happen at the ballet, at the movies, when she is on a book tour and when she's visiting one of New York's public schools.

Ms. Kennedy is said to be patient and gracious during these encounters, leaving the other person feeling as if he or she has had a significant conversation.

Sounds like perfect training for an ambassador.

Ms. Kennedy, 55, has been nominated to be the next United States ambassador to Japan.

As an old family friend, the director Mike Nichols, said, it's a job for which Ms. Kennedy is ideally suited. After all, he said, "In the course of her life, what has she learned if not diplomacy?"

Walter F. Mondale, the vice president under Jimmy Carter and the ambassador to Japan from 1993 to 1996, said that Ms. Kennedy's famous last name should serve her well.

"They love the Kennedys over there," he said. "They've worked with several of them, and they appreciate their position in public life. They know she's an American star, and they know she's a serious person and that she'll be well prepared."

Said Kenneth R. Feinberg, the head of the John F. Kennedy library: "As the sole surviving member of President Kennedy's family, she is the guardian of the flame. It is an awesome responsibility, and she does it extremely well."

The diplomatic post would also give her the chance to serve President Obama, whom she endorsed back in January 2008.

At the time, Mr. Obama was in a tight primary with Hillary Rodham Clinton, whose husband, the former president, had enjoyed a warm and longstanding relationship with Ms. Kennedy. But Ms. Kennedy's children were all more enthusiastic about Mr. Obama. And to Ms. Kennedy, who declined to comment for this article, this counted for a lot.

When Mr. Obama won the nomination, Ms. Kennedy was given a leadership role, working on the search committee for the vice presidency.

At home, Ms. Kennedy leads what is by all accounts a quiet existence. Most nights, she is at home with her husband, Edwin Schlossberg, an interactive designer and artist with an interest in progressive design culture. When the couple does entertain, guests come from a variety of fields.

Richard Plepler, the head of HBO, recalled holding a dinner party back in 2003 at which almost all of the guests were in favor of invading Iraq. "The only person at this table who eloquently dissented was Caroline," Mr. Plepler said. "I remember it very vividly, in part because she likes to remind me that she was right and I was wrong. "

Mr. Nichols described going over to Ms. Kennedy's apartment last November to watch the election returns come in. "I walked in, and she said, oh, go find Rupert, he's in the library. It's quiet in there.'"

She was referring to Rupert Murdoch, head of the News Corporation.

"It's the Washington thing: who you work for, what your beliefs are entirely beside the point," Mr. Nichols said of Ms. Kennedy's attitude.

And that's part of what he thinks will serve Ms. Kennedy well in her position in Japan, where she would likely do everything from entertaining at the embassy to meeting with foreign dignitaries and politicians with a variety of ideological persuasions. "If anybody knows those rules," Mr. Nichols said, "it's her."

The New York Times