PITTSBURGH (AP) _ Two teen-age girls joked and laughed during their arraignment on criminal homicide charges in the death of a 91-year-old woman who was robbed, bound and abandoned for four days, an official said.

Marcella Chambers, who was discovered Jan. 18 lying on her bathroom floor with her wrists tied, died Monday of heart failure at Suburban General Hospital, officials said.

Tamara Liggins, 14, and Kristin Rice, 15, wards of the state who lived at a center for abused and neglected children, were charged in the death, said Allegheny County Deputy Coroner Ed Capretta.

Also charged was Wayne Mialki, 16, who lived near the victim in suburban Ben Avon, Capretta said.

The girls appeared ''very jovial'' during Tuesday's arraignment, Capretta said.

''They were kidding around,'' he said. ''When they were told the news media was out there, one girl started posing.''

But Capretta said Mialki ''was pretty somber.''

The two girls had been reported as runaways from the Holy Family Institute in Emsworth on Jan. 13, a day before Mrs. Chambers was attacked, said Sister Theresine Spellacy, the institute's executive director.

The three are being held at the Shuman Juvenile Detention Center to await a coroner's inquest Feb. 6. It was not immediately known whether they would be tried as juveniles or adults.

The two girls were charged last week with robbery, burglary, conspiracy and reckless endangerment, said county police spokesman Walter Alberts. Mialki had been charged with robbery, burglary and aggravated assault.

All three attended Avonworth Senior High School, officials said.

Mrs. Chambers was discovered by police after a man who was renting her garage became concerned when he did not see her for some time.

The intruders bound Mrs. Chambers and made off with jewelry and an undetermined amount of cash, Alberts said.