When the bus Sidney Dorros was riding pulled up to his stop, he couldn't get off. In fact, he couldn't move. A victim of Parkinson's disease, he had miscalculated the time it took for his medication to work and the affliction had frozen him in place. So he stayed on the bus and rode to the end of the line. By the time he got to his stop for the second time he had "thawed out" enough to get off.

One of Dorros' close friends, Robert Miner, pondered the experience.

"Just imagine what it would mean--20 miles from home and all of a sudden you just get stiffer than a board." Think, said Miner, of the loss of dignity, of the fear.

"A lot of people in his condition probably would say, 'I just can't do those things,' but he takes those chances all the time. He is probably the most courageous man I ever met."

Dorros, 56, is more apt to describe himself as "practical" or "realistic." Incidents like the one on the bus happen less frequently these days, he said, because the medicine he now takes is more predictable.

Because emotions, diet and exercise can affect his medication, however, Dorros can never completely predict how his body will respond. So, calculating the odds the best he can, Dorros ventures out into the world.

Dorros has learned to "accommodate" himself to his disease, but not to "surrender," he explained.

"You have to accept your limitations," he said, but at the same time "you have to learn to make maximum use of your remaining abilities."

Dorros will be the first to tell you he hasn't always felt that way about Parkinson's disease. When his illness was first diagnosed almost 20 years ago, he recalled, "I used to curse God," daring him to "strike me dead."

An otherwise healthy "workaholic" with a rising career at the National Education Association and a young, growing family, Dorros had contracted a crippling disease that usually strikes people over 60. It took him more than a year to adjust to the idea, he said.

Parkinson's, he soon learned, is one of the most common disorders of the nervous system among older people and its main symptoms are uncontrollable tremors in the arms and legs, muscle rigidity, difficulty in starting movement and mental depression.

As the disease progresses, he was told, patients usually develop stooped posture, loss of facial expression, a shuffling gait and increasing difficulty in walking, talking, writing, and all other tasks requiring muscular coordination.

The cause of Dorros' form of Parkinson's is unknown and there is no cure. Asked for a prognosis, Dorros' neurologist could only tell him: "You'll probably die of something else before parkinsonism gets you. In the meantime, make the most of life while you can."

In a book that took him eight years to complete, Dorros describes how he gradually learned to accept that advice. Published recently by Seven Locks Press of Cabin John, Md., "Parkinson's: A Patient's View," traces Dorros' struggle with the disease from the time he felt the first ache in his left shoulder while raking leaves through the worsening of the illness to his desperate search for cures and treatment.

"I felt even if it didn't get published it could be of value to my friends and family," he says.

One of Dorros' physicians, Dr. Donald Calne, formerly clinical director of the National Institute of Neurological and Communicative Disorders and Stroke at the National Institutes of Health, praised the book. It "fulfills the need for an articulate and comprehensive record of a patient's experiences in parkinsonism and its treatment," Calne wrote in the preface.

Noting that the book gives an unusual insight into "what it is like to be on the receiving end" of treatment, Calne recommends it to Parkinson's patients, their families and doctors.

As his disease progressed, Dorros wrote, it reduced him three times to "almost complete incapacitation and abject depression," but each time he "experienced dramatic rescues by modern medicine."

One of those rescues was a new and delicate brain operation. The other two involved treatment with then-experimental drugs L-Dopa and bromocriptine at NIH.

Dorros' book describes in candid detail his 12-year experience as an experimental patient at NIH. He is one of the first and longest-living parkinsonians to be treated with those drugs.

Neither of the two drugs Dorros was given at NIH nor the refined version of L-Dopa he now takes, called Sinemet, has restored complete coordination. And to get relief, Dorros must take his medication every two hours, being careful not to underdose or overdose himself.

Too little medicine causes him to freeze up--like the time on the bus--while too much causes uncontrolled movements called dyskinesia. Since it takes the medication about a half hour to work, Dorros must always plan ahead.

Dorros discusses how he learned to juggle the medication's effects, adapting virtually all his daily activities from cooking, typing and talking on the phone to using the bathroom and having sexual relations. Learning to cope often called for "the tolerance of considerable embarrassment," he writes.

Dorros also discusses the effects his disease had on his four children--now aged 23 to 32--as they were growing up. He says he has never been able to convince them that Parkinson's is not hereditary, despite strong--though not yet conclusive--scientific evidence showing it is not passed from parent to children.

The fact that both his parents have the disease has not helped his case. His brother, and only sibling, has never shown symptoms of the illness. Some doctors have suggested that Dorros and his parents may have been exposed to something in the environment through which they contracted the disease.

Not surprisingly, Dorros' illness put a great strain on his marriage. He writes compassionately about how difficult it was for his wife to live "with a husband whose frustrating, mysterious illness often made him seem a frightening stranger." During his illness Dorros became very dependent on his wife, a registered nurse, to "run our household, solve family problems, maintain social relationships, transport me around and cope with the many problems of my illness."

About three years ago his wife became terminally ill with breast cancer.

"I had thought that I couldn't manage without her help, but she became so ill that I felt the need to reverse roles and take care of her. The new relationship revived her feeling of love and respect for me. Her expressions of love had a strong therapeutic effect which continued even after her death," Dorros writes.

As often happens with traumatic events, Dorros' illness and his wife's death prompted him to reexamine his life.

"Throughout my career I had consciously or subconsciously chosen to work much harder than was demanded of me," he recalls.

First as a teacher, then a vice-principal and a principal, later as communications and research director of the Maryland State Teacher Association and finally as director of the publications division of the NEA, Dorros worked long, intense hours. Even after being diagnosed as parkinsonian, he completed his PhD in education at George Washington University.

More than 10 years after his diagnosis, Dorros was still working full time at the NEA.

Although he was finding it more and more difficult to concentrate and make decisions and despite the fact that friends had to transport him to and from work, Dorros continued putting in a full day. It all ended eight years ago when he froze up during a meeting and became so stiff that he couldn't get his pills out of his pocket. On Sept. 1, 1973, Dorros officially retired on disability at the age of 48.

Dorros says his ability to adjust to his illness was due in large part to emotional support from friends and family. "As I look back at my life I see the power of love as important as any drugs in helping me cope with parkinsonism," he writes.

It has also helped him to keep busy. He lived alone until recently when his younger daughter graduated from college and moved back in with him, but he is still independent, filling his days with shopping, cooking, exercising and working on his various outside activities.

Around the time of his wife's death, Dorros helped to start and became the first president of the Parkinsonian Society of Greater Washington.

Overall, Dorros says, being a sick man has helped him develop a keener appreciation of life. When you are ill "everything become more precious, the stakes are higher. . . . I'm certainly not glad I got Parkinson's but I am happier now than when I had everything to live for."