In a halting, tearful admission, a mother accused of overdosing her 10-month-old daughter on methadone pleaded guilty yesterday to voluntary manslaughter and cruelty to children.

Tracey L. Cobb, 38, struggled to tell the judge that she wanted to enter a plea in the case, which was brought against her in March after the death of her baby girl, who was born dependent on methadone.

"Do you need more time?" Judge Ann O'Regan Keary asked Cobb, who had gone silent during one of several emotional pauses in the hearing in D.C. Superior Court.

Comforted by her attorney, Claudia Crichlow of the D.C. Public Defender Service, Cobb finally nodded, fighting back tears and dabbing her eyes with a tissue

"Yes," she wanted to plead guilty, she told Keary.

Cobb, who was arrested March 24 at her home in the 1600 block of Sixth Street NW, originally was charged with murder in the Feb. 1 death of her daughter, Symphony Jenkins. She has been jailed since her arrest.

Cobb took methadone during her pregnancy to shake off her addiction to heroin, and that led to Symphony's dependence on the drug, officials said. The D.C. child welfare agency launched an investigation after Symphony was born in March 2003. Several months later, the agency closed the case after concluding that the baby was well cared for and that other city agencies were helping the family, officials said.

Ordinarily, a newborn can be weaned off methadone within several days, but that apparently did not happen with Symphony.

Soon after the baby was brought home from the hospital, Cobb began using a medicine dropper to add methadone to Symphony's formula, after seeing the child's godmother give the baby a dose of the drug, prosecutors said. After her arrest, Cobb told investigators that she gave Symphony the drug two or three times a week.

Cobb was receiving methadone through a treatment program run on the campus of D.C. General Hospital. A synthetic drug, methadone is used to help addicts get off heroin because it prevents withdrawal symptoms and does not produce a heroin high.

The methadone was only for Cobb, and she never should have given it to her daughter, even if her intention was to make the girl "feel better," Assistant U.S. Attorney Gregory G. Marshall said yesterday in court.

"She knew that her conduct was wrong and dangerous," Marshall said in outlining what he would have presented had the case gone to trial.

Ultimately, the conduct proved to be deadly.

On or about Jan. 31, according to prosecutors, Cobb administered a "larger-than-usual dose of methadone" to the baby. Found unconscious the morning of Feb. 1, Symphony was taken to Children's Hospital, where she was pronounced dead an hour later. The D.C. medical examiner determined that she died of methadone intoxication.

Cobb could be imprisoned for up to 45 years when she is sentenced by Keary on Aug. 6.