By Brian C. Mooney In a life lived mostly out of the spotlight, Jean Kennedy Smith had a close bond with the brother she buried yesterday in Arlington National Cemetery.

Now 81, Kennedy Smith is the last living child of Joseph and Rose Kennedy, the final link to an extraordinary constellation of siblings who left an indelible mark on postwar America. Since Edward M. Kennedy’s death Tuesday, Kennedy Smith, along with the senator’s wife, Victoria Reggie Kennedy, has led the extended Kennedy family in mourning.

“Jean, I know you lost your soul mate,’’ Kennedy’s niece, Caroline, told her at Friday night’s memorial service at the John F. Kennedy Presidential Library and Museum. “All your nieces and nephews are here to help you as best we can.’’

Kennedy Smith was the eighth of nine children; Edward Kennedy was the youngest, born four years later. She introduced him to his first wife, Joan, and, when she was 65, her brother prevailed on President Clinton to name Kennedy Smith ambassador to Ireland.

When their sister Eunice Kennedy Shriver died two weeks before the senator, Kennedy Smith stayed with her brother, whose failing health prevented him from attending the funeral.

“Jean always had a special relationship with Teddy,’’ their mother wrote in her 1974 memoir, “Times to Remember.’’

“They were a pair; they trotted around together; she sometimes admonished him and sometimes scrapped with him but mainly was his valiant friend and big sister,’’ she wrote.��’ she wrote. “She still is, though he is now nearly twice as big as she is.’’

Kennedy Smith worked on the campaigns of her brothers John, Robert, and Edward, and she accompanied President Kennedy on his famous visit to Ireland in 1963, five months before his assassination.

She is best known for her service as ambassador to Ireland, from 1993 to 1998, when she played a significant and controversial role in advancing the cause of peace in Northern Ireland. In 1994, over the objections of the British and members of her own staff, Kennedy Smith strongly urged the State Department to allow a US visit by Gerry Adams, the leader of Sinn Fein, the political arm of the Irish Republican Army. The IRA later declared a cease-fire, and the visa is viewed as a factor in that decision.

Two years later, however, Kennedy Smith was reprimanded by the secretary of state of the time, Warren Christopher, for retaliating against a pair of subordinates who had objected to granting Adams a visa.

She also raised diplomatic eyebrows by taking Communion in an Anglican church in support of the Irish president, Mary McAleese, who was being criticized for doing the same in an effort to promote religious tolerance.

“There’s no ambiguity about the Kennedys in Ireland, so doors opened for her,’’ said Maurice Mannin�� said Maurice Manning, who was leader of the Seanad, Ireland’s senate, at the time. “She was a very unorthodox ambassador, at times annoying people in government because she had her own agenda, which was essentially to bring Gerry Adams and company in from the cold. She was hugely successful and hugely influential in doing that.’’ Manning, who is now chancellor of the National University of Ireland, said, “There’s a quietness and charm but also a toughness and single-mindedness to Kennedy Smith.’’ She was also, Manning said, “very socially gregarious and gave the best parties of any ambassadors anywhere. People fought to get into her place’’ at Dublin’s Phoenix Park.

As Kennedy Smith prepared to return to the United States, McAleese bestowed on her honorary citizenship in the country that her great-grandfather, Patrick Kennedy, had left 150 years earlier.

Like her mother, Kennedy Smith was educated at schools run by the Society of the Sacred Heart of Jesus. These included convent schools in the United States and England and her mother’s alma mater, Manhattanville College in Purchase, N.Y. At Manhattanville, her roommate was Ethel Skakel, whom she introduced to her older brother, Robert. Later, she introduced a younger Manhattanville student, Joan Bennett, to brother Ted, and they were engaged not long after.

Kennedy Smith married Stephen E. Smith, who grew up in Brooklyn in a wealthy family that made a fortune in the tugboat and barge business in New York. Smith, who died of cancer in 1990, was a major behind-the-scenes figure in the Kennedy family, managing political campaigns, the family finances, and the effort to build the Kennedy Library. The couple lived in Washington and New York’s Upper East Side and raised two biological sons and two adopted daughters.

Their second oldest, William Kennedy Smith, a physician whose practice focuses on victims of landmines, was acquitted in 1991 of charges he raped a woman in Palm Beach, Fla., after a night of drinking with his uncle Ted and cousin Patrick Kennedy.

While her sister Eunice won acclaim for establishing and promoting the Special Olympics, which has changed perceptions of the mentally challenged, Kennedy Smith in 1974 established VSA Arts, which promotes learning and education through the arts for people with disabilities in more than 50 countries. In 1993, she co-wrote with George Plympton “Chronicles of Courage: Very Special Artists.’’

Besides VSA, she has promoted and raised funds for causes and philanthropies ranging from international peace to Irish immigration.

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