Elizabeth Ann Harris, 12, was running toward the front door of her parents' University Park home Wednesday when she slipped and fell through the glass of the storm door. Prince George's County police reported yesterday.

As she landed, a jagged piece of glass pierced her chest, severing a major artery near her heart. She was pronounced dead at Prince George's Hospital less than an hour later.

"We just couldn't understand what in the world happened," an 80-year-old neighbor of the Harris family said yesterday after hearing of the bizarre accident. "She was one of the sweetest girls I ever knew," added Carroll Lewis, who lived down the street from the Harris home at 6703 44th Ave.

"She was a brilliant child, too. You could talk to her about anything and she'd want to talk about it," Lewis said. "She was always playing. She was full of life."

Elizabeth Harris, known as Beth, was just finishing seventh grade at Hyattsville Junior High School.

"I used to teach her gymnastics when she was in elementary school," said another neighbor, 19-year-old Cindy Kisielmicki. "She was the type of kid who you'd say 'Why don't you try this?" to, and she would always try it."

". . . If she didn't do it right, she would come back and try it again until she did."

Neighbors said that Beth Harris, who had short brown hair and brown eyes, was also a member of the Daughters of the American Revolution. She was one of five children of Phillip W. and Florence Ann Harris.

According to police, the girl had been running outdoors when the accident occurred. She reached for the handle of the storm door, they said, missed it, and put her hand through the glass of the door.

She then fell through the broken door, landing on a piece of glass that severed her aorta.

"We loved her like she was our own child," said Lewis, her neighbor. At the age of four, Beth Harris had been a flower girl at his daughter's wedding.

"We've had accidents like this happen before," Prince George's County police Sgt. Robert Law said yesterday, "but very seldom do they ever end this tragically." CAPTION: Picture, ELIZABETH ANN HARRIS . . . was running outdoors