A 15-year-old Springfield girl, reportedly despondent over a poor report card and the death of the family dog, walked into a bathroom of her home Friday night and set herself on fire.

Officials at Washington Hospital Center said yesterday that the victim was in very critical condition with burns over 85 percent of her body.

The girl, a sophomore at Annandale High School, was flown to the hospital's burn unit by a National Park Service helicopter after a neighbor found her engulfed in flames in the family's splitlevel home in the Ravensworth Farms subdivision.

Fairfax County police said the victim apparently had doused herself with turpentine then lit a match in an attempt to take her own life. Neighbors said the girl's mother was at work at the time but that her 13-year-old sister heard her screams and summoned a neighbor.

The neighbor rushed into the house and threw a blanket on the girl, extinguishing the fire that engulfed the jogging suit she was wearing.

Friends of the victim said she was a "happy-go-lucky" individual, but had been quieter than usual during recent weeks, grieving over the loss of her 14-year-old mongrel dog, who had recently died of the deadly canine disease, parvo virus. On Friday, the friends said, the girl became more anguished after she received a report card with a failing grade in geometry.

Neighbors in the hilly subdivision located just outside of the Capital Beltway said they were shocked by the incident and several people could not believe the police account that she attempted to take her own life. "I would never in a million years imagine she could do something like this to herself," said one neighbor, a close friend of the girl's mother.

"She had a lot of friends . . . nobody can believe she would do something like this," agreed a teen-aged friend.

Like other youngsters in the neighbornood, the victim spent much of the past summer at the community pool where she was fond of "showing off" her expert diving skills to spectators. A recent leg injury that prevented her from qualifying for the Annandale High School diving team may also have contributed to some of the girl's depression, others said.