Mary Livingstone, 77, the wife and partner in comedy of the late Jack Benny, died today at her home here, apparently of a heart attack.

She had been retired from show business for nearly a quarter-century, and had lived alone except for servants since Benny's death in 1974.

Born Sadye Marks in Seattle, she met Benny in a Los Angeles department store in 1926, and the couple was married a year later. She appeared intermittently in her husband's stage act over the next few years, but considered herself primarily a housewife until Benny became the star of his own radio show.

For one program, the scriptwriters found themselves unable to fill a bit part: that of a girl who came on and read some silly poetry. The name in the script was 'Mary Livingstone.' "

Miss Livingstone filled in, and listener response was so unusual that "Mary Livingstone" became a continuing role. It also became her real name in 1949, when she made the change legal because "even my husband calls me 'Mary.' "

She continued on the enormously popular radio show into the 1950s, and stayed on as "The Jack Benny Show" moved to television. As the years passed, however, her interest in her own career waned.

"It ended up with every Sunday night being the most torturous day of the week," she once said. "TV was even harder; every week became a nightmare. I finally just told Jack I was going to quit or I was going to die."