BOSTON — Patricia Kennedy Lawford, the sister of President Kennedy whose marriage to Peter Lawford lent Hollywood glamour and Rat Pack cool to her family's political dynasty, has died. She was 82.

Lawford died Sunday of complications from pneumonia at her New York home, brother Sen. Edward M. Kennedy of Massachusetts said through a spokeswoman.

"My sister Pat is irreplaceable," Kennedy said. "Everyone who knew Pat adored her. She was admired for her great style, for her love and support of the arts, her wit and generosity -- and for the singular sense of wonder and joy she brought into our lives."

In his 2005 best-seller, "Symptoms of Withdrawal," her actor son, Christopher Lawford, wrote of his mother that "her lightheartedness and vibrancy made her my grandfather's favorite." But he said she also felt resentment toward her father "at not being allowed fully to live up to her potential."

She met the handsome British-born actor Peter Lawford through her brother, the future president, in 1949. They were married in 1954 and had four children.

Lawford is best known for roles in such musicals as "Easter Parade" (1948) and "Royal Wedding" (1951), both with Fred Astaire, the 1954 Judy Holliday comedy, "It Should Happen to You," and "Exodus" (1960), with Paul Newman.

In the late '50s and early '60s, he was a member of Frank Sinatra's circle of friends dubbed the Rat Pack, appearing in the original version of "Ocean's Eleven" in 1960. It was a link that brought a touch of Hollywood glamour to Sen. Kennedy's presidential campaign that year.

Christopher Lawford wrote that Sinatra, Judy Garland, Henry Fonda and Milton Berle used to drop by the Lawford family's California beachfront home and that his mother thought of Marilyn Monroe as "her little sister."

But the Lawford-Kennedy marriage was troubled and ended in 1965 in a bitter divorce, the first for a member of the staunchly Roman Catholic Kennedy clan.

Laurence Leamer, author of "The Kennedy Women," said that Patricia Lawford couldn't handle her husband's philandering and well-documented drinking and drug use.

"When she married Peter Lawford she was very much an innocent thrown into this world of incessant liquor and blatant sexuality and drugs," Leamer said in a telephone interview.

Leamer said Patricia Lawford was driven to alcoholism herself by her failed marriage and her brother's death in 1963.

"She was the gentlest, the sweetest of all the Kennedy sisters, and she suffered the most from the assassination of her brother," he said.

Patricia Kennedy was the sixth child and fourth daughter among Rose and Joseph Kennedy's nine children.

Inspired by her father's career in the movie industry, she set her sights on Hollywood soon after her graduation from Rosemont College, a Catholic liberal arts college.

She began working as an assistant in NBC's New York production department and then moved to Los Angeles with the goal of becoming a producer and director. She worked as an assistant for Kate Smith's radio program and for Father Peyton's Family Theater and Family Rosary Crusade, where the slogan "The Family that Prays Together Stays Together" was coined.

Patricia Lawford traveled the country in support of her brother's presidential campaign in 1960 and was involved in the political campaigns of brothers Robert and Edward.

She was at Robert Kennedy's bedside when he died after being shot by Sirhan Sirhan in June 1968.

After her divorce, she moved to New York, where she became a supporter of the arts. She founded the National Committee for the Literary Arts at Lincoln Center and worked with the National Center on Addiction and Substance Abuse at Columbia University and the Kennedy Library.

Joseph Califano Jr., president of the addiction center, called her "a great friend, who with a marvelous sense of humor helped make the world a better place for all of us."

Kennedy Library Chairman Paul Kirk Jr. said in a statement, "Whether she was personally overseeing the refurbishing of the library's formal reception room, representing the Kennedy family at public events and ceremonies or being fully engaged at board meetings, Pat Lawford embraced the mission of making the Kennedy Library a living and vibrant memorial to her brothers John and Robert."

Besides her son and brother, survivors include daughters Sydney, Victoria and Robin; 10 grandchildren; and sisters Eunice Kennedy Shriver and Jean Kennedy Smith. Memorial and funeral arrangements were pending.