PHILADELPHIA -- Marge Torre was a typical 7-year-old in 1945. She loved to run, romping on playgrounds and playing hide-and-seek with the other kids on her street in southwest Philadelphia. Then polio cut her childhood short.

The disease ravaged her lower legs. She had surgery more than 20 times, spent weeks and months in hospital wards, and wore orthopedic braces on both legs for the next 10 years. Finally, when Torre was 17, the braces came off. She was free.

Until three months ago.

In late September, after months of extreme, constant exhaustion in her legs, Torre's doctor told her she would have to start wearing the braces again. "The devastation came when they actually put the braces on," she said. "It was like I was a little kid again, and the only thing ahead of me was all those operations, all that pain and suffering."

Torre is one of thousands of polio survivors who are having to do battle again with their old nemesis. They are suffering from post-polio syndrome, sometimes called post-polio muscle atrophy.

According to the International Polio Network, an information and referral service in St. Louis, the number of people stricken with post-polio syndrome has been growing steadily since the disease was first diagnosed in the early 1980s.

Dr. Mary Ann Keenan, chairman of the department of orthopedic surgery at Albert Einstein Medical Center in Philadelphia and a nationally respected authority on post-polio syndrome, says she averages two new patients a week with post-polio syndrome.

"I expect that number to grow astronomically, exponentially," said Keenan, 40, who studied under Dr. Jacquelin Perry, regarded by many as the nation's top polio expert, at Rancho Los Amigos Medical Center in Downey, Calif.

"People got by for 20 or 30 years, then gradually they were coming back saying, 'I thought the polio was all gone,'" Keenan said. "Or, 'My right leg was normal. Now, it's getting very bad.' "

Post-polio syndrome is not a recurrence of polio. It is thought to be caused by polio survivors overusing the motor nerve cells, or motor neurons, that stimulate muscle tissue.

Polio, or poliomyelitis, is an inflammation of that part of the spinal cord containing the motor neurons. It is thought that post-polio syndrome occurs because the motor neurons unaffected by polio must overcompensate for those destroyed by the disease, leading to a gradual deterioration of muscle tissue.

No one knows how many people are affected.

Joan Headley, executive director of the International Polio Network, said the federal Centers for Disease Control estimate that there are 250,000 polio survivors in the nation; the National Center for Health Statistics puts the number at 650,000. She said health professionals expect 40 percent of polio survivors to suffer post-polio syndrome.

Because polio was all but eradicated in the United States after a vaccine was introduced in 1955, Keenan said, not many doctors today have specialized knowledge about it.

"The first problem people with post-polio syndrome faced was that all the people {physicians} who knew about polio had died or had quit practicing," she said. Headley's agency lists only 60 clinics and 100 doctors around the country as "knowledgeable" about polio, including Keenan and three other physicians in Philadelphia.

Keenan, who is also director of orthopedic surgery at Moss Rehabilitation Hospital in Philadelphia, studies post-polio syndrome patients at that hospital's Gait Laboratory.

She and Dr. Alberto Esquenzai, director of the laboratory, put patients through a series of tests on sophisticated, computerized equipment to determine which muscles are weak and how to brace the legs most effectively.

Keenan advises her post-polio syndrome patients to use their energy wisely, to plan ahead for strenuous activities. She estimates that surgery is necessary for about 10 percent of people with post-polio syndrome. Most people can correct the problem by limiting and modifying their activities, or with braces.

Perhaps the most troubling for some post-polio syndrome sufferers is the psychological trauma of having to reach back for an orthopedic aid -- a cane, a wheelchair or braces. The reaching back, they say, conjures painful memories.

Even now, a lifetime later, Torre can describe in excruciating detail her last real day of childhood. She's pretty sure it was a Sunday.

"The night before they took me to the doctor, my daddy said if I would go around the corner to get him a ginger ale, he would get me a double-decker ice cream," she said.

On the way home from the store, the pain she had been feeling in her legs for three days stopped her on the curb in front of her house. She couldn't get across the curb, couldn't make her legs work through the pain. A neighbor carried her inside.

The next day, Torre was diagnosed with polio. She spent 10 days in isolation at Municipal Hospital, then was treated at Children's Hospital of Philadelphia and later at Shriners Hospital. She says she stopped counting after her 20th operation.

Today, Torre is chairwoman of the March of Dimes' health professional advisory committee. She lobbied extensively and successfully for pre-age-65 Social Security benefits for post-polio syndrome sufferers.

She expends much of her precious energy in service to others -- doing radio talk shows, preparing informational brochures, getting the word out. Torre is cheerful, upbeat, sometimes determinedly so.

But now and then, in one of her rare moments of motionlessness, she seems pensive, thoughtful. And you wonder whether she moves about so much simply because she can move about. You wonder if she's seeing the little girl from Catharine Street who lost her freedom to run.