Margo Skinner, one of the four cast members of the Manhattan Theatre Club production of Moonlight and Magnolias, died suddenly yesterday at age 55.

No cause of death could immediately be determined. Skinner's understudy, Karen Trott, will assume the role of David O. Selznick's secretary, Miss Poppenghul, in Ron Hutchinson's play about the re-writing of the screenplay for Gone With the Wind.

Skinner received a B.A. from Boston University. Her stage credits include tours of Titanic and I Never Sang for My Father, as well as Off-Broadway productions of The Perfect Party, The Dining Room, and Blue Window. She also performed at many regional theaters, including Atlanta's Alliance Theatre, the Guthrie in Minneapolis, and the Geffen Playhouse in Los Angeles.

She is survived by two sisters, a nephew, and her companion, Andrew Macagnone.