Two young children who were found dead in a closet in a Herndon town house Sunday appeared to have been strangled, a Fairfax County prosecutor said yesterday at the arraignment of the children's mother, who has been charged with murder.

Nhoeung Khlaut, 29, who relatives said in an interview yesterday complained she heard a constant voice "calling her stupid," was arrested Sunday after the bodies of her 4-year-old son, Thi Nguyen, and her 11-month-old daughter, Vuy Thi Mihn Nguyen, were found in a downstairs closet at a relative's town house in the 2100 block of Ferguson Place in Herndon.

Deputy Commonwealth's Attorney Raymond F. Morrogh said marks left on the children's necks were consistent with strangulation. Police said autopsy results are expected today.

Relatives said Khlaut, who lived with her husband in Manassas, had been staying at the house in Herndon since last Tuesday. They said her husband had taken her there to see whether she might escape from an image of a woman with long hair that appeared in her head and constantly called her stupid, her sister, Yarang Khlaut, 36, said yesterday.

Morrogh told Chief Judge Jane P. Delbridge in Juvenile and Domestic Relations District Court that Nhoeung Khlaut had a history of mental problems and could be dangerous to herself and others.

"When she was taken into custody . . . she attempted to swallow her wedding ring," Morrogh told the judge.

Khlaut, a tiny woman dressed in wrinkled blue prison garb, sat in the courtroom with her head bowed, shuddering, wiping tears and shaking her head slightly back and forth. She barely answered as Delbridge, speaking through an interpreter, informed Khlaut of the charges and told her that she would be held without bond.

"She keeps saying she doesn't understand," said the interpreter who spoke to Khlaut in Khmer, her native language of Cambodia.

Yarang Khlaut said in an interview that her sister began hearing voices about a year ago and gradually reached a point where she did not recognize her family. "When we ask her, 'Do you know who I am?' she said, no, she doesn't know anybody. She doesn't know her sister. She doesn't know her husband. She said, 'No, I don't know you,' in a deep strange voice."

Yarang Khlaut said her sister did not improve after she moved out of her house in Manassas. "Her husband tried to bring her here to make her better, but everywhere she goes she hears, 'You stupid. You stupid.' She never got help."

Khlaut said the woman's husband took her to a doctor recently but that the doctor said he found nothing wrong with her. Khlaut said she did not know the doctor's specialty.

Yarang Khlaut's husband, Bany Kong, said in an interview that their 9-year-old daughter, Mary Anne Kong, found Nhoeung Khlaut hiding behind an ironing board in a downstairs closet Sunday morning.

Mary Anne opened the door of the closet yesterday and pointed to where she found her aunt, then farther back at the space where the children's bodies were lying in blood.

Fairfax police say the slayings of the children pushed the county's homicide toll to 15 this year.

Lt. J.A. Vickery, spokesman for the Sheriff's Department, said Khlaut was being held yesterday in special isolation at the county jail, where she was being evaluated by the jail's forensic staff and awaiting appointment of an attorney.

Yesterday, a brown paper bag with the children's clothes neatly folded and the boy's favorite toy, a jack in the box, waited for the father to pick them up.

"I still feel not good," Yarang Khlaut said. "I miss them so much."

"I'm very hurt because I lost my two children," said Duong Nguyen, the children's father, in a telephone interview. "It feels like someone shot me."