Worried whispers followed Fran Bonaiuto as she walked down the corridors of Robert E. Peary High School in Rockville, her tiny frame always huddled in a beige parka. The 30-year-old Spanish teacher had looked gaunt for years, but this fall people noticed the contours of her skull showing through her skin.

Then, when she failed to arrive for her first-period class last Monday, the principal called police. She hadn't missed a day of school in seven years.

The police found her body lying between the kitchen and bedroom of her Silver Spring apartment. She had been dead two days.

Miss B. as her students called her, weighed only 57 pounds.

Police found no marks on the body and no sign of violence in the apartment. Bonaiuto's death certificate in the state medical examiner's office listed no cause of death. An autopsy report may take four to six weeks.

Whatever the coroner eventually rules, her friends believe she starved to death.

Bonaiuto's physician, Dr. Richard P. Delaney of Silver Spring, said he thinks she suffered from anorexia nervosa, a rare mental disorder characterized by obsessive dieting. Bonaiuto herself told friends she had a thyroid condition. Dr. Delaney said he is not sure what caused her death.

"She never got far enough into the medical system for anybody to find out what she had," Delaney said. "I'd really thought we'd be able to get her into the hospital and treat her. I thought we had time to do this."

Delaney said he hoped to persuade her to enter a hospital on Friday, but she didn't live that long.

Anorexia, Delaney said, often strikes young, intelligent women.

"That's not what my daughter had," Bonaiuto's mother, Mary said yesterday from her home in Middletown, Conn. "She was always slim. She always wanted to be a little heavier."

At the Artic Avenue school where Francis Mary Bonaiuto came to teach in 1973, grief mingled with frustration as teachers and students remembered their last months with Miss B. They had watched her dying and they had felt powerless to prevent it.

"I told one teacher that I didn't think Fran could last till Christmas," said Peary's assistant principal, Audrey Leslie. "For years people tried to get her to come home with them, but wherever food was involved, she would have no part of it."

There was one symptom painfully apparent to the students and teachers who knew her: Miss B. almost never ate.

"At lunch break," said sophomore Paul Nisson, "she would go upstairs to the bathroom and then would walk back and sit at her desk with her head down."

Another student, senior Sue Lamoureux, often ran errands for her Spanish teacher and sometimes stopped by her apartment to visit. "Her toaster," Lamoureux remembered, "looked like it had never been used. And there was nothing on the counter."

All police found in her refrigerator were several containers of yogurt, a package of frozen meat patties, some ice cream, coffee and many cans of Faygo diet soda.

She had so little fat on her body, that she couldn't resist the cold. The thermostat in her apartment was set at 85 degrees.

At school, teachers, and friends recalled Miss B's constant effort to stay warm. In her classroom in the basement of the rundown high school, she wore her parka with the hood up and a scarf wrapped around her neck. On her legs, which a friend said were no bigger than a woman's forearms, she wore long underware under her blue jeans. And there were always gloves on her hands.

"She said she could stand pain, she could stand anything," Lamoureux recalled. "She said nothing would make her cry but being cold."

In the weeks before the Thanksgiving holiday, concern for Bonaiuto's health began to deepen. This fall the temperature in the school had been lowered three degrees, to 65, and Bonaiuto's skin had acquired a gray cast and a parchment-like-texture. Friends noticed that she seemed more withdrawn than in the past.

"I've seen pictures of victims of Auschwitz who looked better," said Leslie.

A snapshot of Bonaiuto appeared once in the 1974 edition of the Peary yearbook Polaris, but after that, she refused to allow pictures to be taken of her.

She had lost so much weight that she put pads in her pants so she could sit without pain.

About three weeks ago Miss B was called in to meet with Leslie and principal Richard A. Dumais, who suggested she seek counseling in the county's employe assistance program.

"She was so intense regarding her job that just the suggestion she talk to people in the employee assistance program made her afraid that she wouldn't be allowed to teach," Dumais said. " Our concern was with her health, not her teaching. She was an exellent teacher."

After the meeting, Bonaiuto seemed "kind of relieved," Leslie said. "She said 'Maybe this is what I need to do.'"

She saw the doctor once a week. "I didn't realize she was in as bad shape as she was," Delaney said yesterday. He recalled having to coax her onto the scale. Three weeks ago she weighed 58 pounds.

Delaney said he'd planned to have her see a consultant, and would try to persuade her to go to the hospital for tests and intravenous feeding.

"I think she would have gone," he said. "She always knew she was sick. It was a matter of timing and nothing but that.

"Everyone loved this girl including me."

On her last day of teaching, the Wednesday before Thanksgiving, she went to see Dumais and said she was getting better.

"She had me feel her hands," Dumais said. "She wanted to show me how warm they were. She said how she felt well and was going to have a good Thanksgiving . . . She talked about the power of prayer."

"I asked her to come have Thanksgiving we me," Leslie said. But she said no she was going to be with friends. said, Fran I don't care where you go, just eat a big meal,' and I hugged her. She was so thin I could have picked her up."

She said two things to her last class that Wednesday, her students recalled. She urged them to "eat as though this Thanksgiving would be your last," and she said that when she came back Monday, she would be completely well.

She drove home in the small Pontiac she only used to get to school and to go each Sunday to St. Jude's Catholic Church on Veirs Mill Road. St. Jude is the patron saint of those suffering from desperate illness.

At Peary High School Friday morning, there was a five-minute memorial service for Fran Bonaiuto coinciding with the time of her burial in Middletown.

The priest from her church read a psalm over the public address system and said a brief prayer.

Later, people talked about the woman few had really known, but many loved noneheless.

"She was the best teacher they've ever had here," said Sue Lamoureux. "She put her whole life into the school."

For her friends and colleagues, it also was a time to ponder whay they might have done to help.

"She died alone on Thanksgiving when family and friends were all together," said English teacher Stanton Boteler.

"I don't know what we could have done," sdaid Leslie, who remembered her first day at Peary High School, when Bonaiuto had brought her a gift of expensive coffees. "It would have made her very unhappy to force her to do something.

"If there's any beauty in this, it's that she taught with great vigor and the full capacity of her brain to the very end. At least she had that."