Maura O'Donnell had succeeded as an athlete and a scholar. Her dream friends said, was to become a nurse so that she might help children with chronic diseases, particularly cystic fibrosis.

Thursday, Maura O'Donnell died at age 20 from the disease she had battled since birth - cystic fibrosis.Death came at the National Institutes of Health.

She was the fourth child Harold and Maureen O'Donnell of Fairfax County had lost to the number one genetic killer of children.

Cystic fibrosis victims' lungs become clogged with a thick mucus with resulting irreversible damage from repeated infections and bouts with pneumonia.

Three times a day for most of her life, Maura had to undergo aerosol inhalation therapy.She put on a face mask, breathed in a medical agent to liquify the mucus and then cleared it from her lungs.

This, along with frequent hospital visits, did not prevent her from attending regular school classes. She was graduated as an honor student from Bishop O'Connell High School in Arlington in 1976.

More important to her, during her four years there, Maura had earned nine varsity letters in field hockey, softball, basketball and diving. She was a state high school diving champion.

She had been a diving coach and instructor, at the Haysfield Swim Club.

The Rev. James McMurtrie, who was principal of O'Connell during Maura's four years there, said yesterday that the field hockey and softball teams always seemed to do better when Maura was playing with them.

"I was the principal and she was the assistant principal, always in my office helping me," he said. "She was not a tragic figure."

"She loved to boogie," he added.

Maura, in fact, had made a splash with her dancing on a number occasions. In March 1976 the first cystic fibrosis "Super Dance" was held at Bishop O'Connell in memory of Brenda O'Donnell, Maura's younger sister. Brenda was a sophomore at the school three years ago when she died of cystic fibrosis at age 16.

Maura danced for 12 hours at that event to help raise the $31,000 that went to the Cystic Fibrosis Foundation's Metropolitan Washington Chapter.

When it was reported the next year, she danced again after addressing a student assembly before the dance. This March she left her bed at NIH to address another student assembly. She danced, but only briefly.

After she finished high school, Maura entered the nursing program at Marymount College in Arlington. She had just completed her second year there when she was hospitalized again on May 7, the day before she was to take her final exams. She had hoped to graduate next May.

"Maura left part of herself in everybody she touched," Frieda Maher, director of health services at Marymount, said yesterday.

"She was full of energy, never bitter. She though she had lived a full life. She was a special person."

"Maura had thousands of friends. She was terrific," said Laurie Barclay, a Marymount student."She was always happy. She gave everybody something to live for," Elizabeth McLaughlin anouther Marymount student said.

"She was the most unselfish human being I have ever met.No matter how sick she was, she always asked first about you," said Gerry Henley, another friend.

Maura was born at the Bethesda Naval Hospital while her father was a Marine Corps officer. He is now retired and teaches history at Flint Hill Preparatory School in Vienna. Her mother teaches Latin at Westminster School in Annandale.

She was diagnosed as having cystic fibrosis when she was only three weeks old. A second sister, Catherine, died in 1962 at age 6. Brenda died in 1975 and a brother, Sean, died in 1976 at age 10.

Two other sisters, Megan, 16, and Bridget, 14, do not suffer from cystic fibrosis. They live at the family home in Springfield, Va.

Mary Grove, director of the Metropolitan Washington Chapter of the Cystic Fibrosis Foundation, said there is a one-in-four chance that a child born to parents carrying the cystic fibrosis gene will have the fatal illness.