A St. Charles woman stabbed two of her three daughters to death and then killed herself with a kitchen knife in her Charles County home, the county sheriff's office reported yesterday.

The woman, Helen Alice Lawthorne, 33, of 213 Garner Ave., Waldorf, had been despondent over marital problems, according to Cpl. Thomas Burch of the sheriff's office.

He said the woman killed her daughters, Maryanne Michelle, 3, and Ann Marie, 7, in their bedrooms Saturday between 10 a.m. and 12 p.m. but heeded the pleas of her 10-year-old daughter to spare her. The surviving girl, Michelle Renee, suffered bruises on the side of her face.

Lawthorne then locked herself in a bedroom and stabbed herself to death, the state medical examiner's office said.

Sheriff's investigators in the community about 20 miles south of Washington said they did not announce the killings until yesterday because they could not locate the woman's husband Preston Edward Lawthorne. They spoke with him Sunday but would not divulge his whereabouts.

The dead woman's mother, who lives in Virginia, called the sheriff's office Saturday at 5:10 p.m., stating that a "possible suicide" had occurred at her daughter's home. Michelle Renee Lawthorne had called her grandmother and told her of the deaths, the sheriff's office said.

The child admitted sheriff's deputies into the home.