Legendary singer and composer Peggy Lee, 81, whose career spanned nearly 50 years, died of a heart attack at her Bel Air home Monday night, her daughter, Nicki Lee Foster, announced on her mother’s Web site. The platinum-haired, silky-voiced star who gave the world the sultry “Fever” and the deeply ironic “Is That All That Is?” — as well as the score to the 1955 Walt Disney animated feature “Lady and the Tramp” — was a diabetic who had suffered a stroke three years ago. “My children . . . and I were comforted by the fact that she was at home, and that I was able to be by her side,” Foster said. Lee’s life was marked by sorrows, and the highs of her career — she wrote for Duke Ellington and Quincy Jones and was a multiple Grammy winner — did little to erase memories of sad beginnings. Born Norma Deloris Engstrom in Jamestown, N.D., Lee was only 4 when her mother died and her father, a handyman and part-time railroad station agent, abandoned her. Stuck with a stepmother who physically abused her, Lee later said she learned to be independent early on. She also memorialized her stepmother in the Calypso number “One Beating a Day,” one of 22 songs she co-wrote for her ill-fated, 1982 autobiographical Broadway musical “Peg.” Early radio appearances gave her the confidence to try Hollywood, where she ended up as a waitress, until bandleader Benny Goodman heard her sing. The hits followed, in particular, “Why Don’t You Do Right?,” which made her a star. The Goodman connection also enabled her to meet the King of Swing’s guitarist, Dave Barbour, whom she married. But when the marriage dissolved, Lee returned to her music. She also received an Academy Award nomination for her role as the hard-drinking singer in the 1955 jazz movie, “Pete Kelly’s Blues.” She was one of a kind.