What could bring Willis Reed, Gerald Ford and Joe Namath to their knees? A new form of exercise?

All three suffer excruciating pain in the patella region due to athletic traumas. In nonmedical jargon, they have bad knees from sports injuries.

Thousands of Americans have bum knees without the glamor of being injured on a football field or a basketball court to fall back on. They may be found cursing on a flight of stairs, standing on the side of a dance floor or taking a bus for two blocks instead of walking.

At first they endure the pain, but when they discover that their knees have swollen, they usually limp off to a doctor.

Dr. John P. Adams, chairman of the Department of Orthopedic Surgery at George Washington University Hospital, has treated patients with knee problems in all age groups.

"Children who are active and even teenagers with malaligned knee joints may experience knee pain, but unless the pain originates from other parts of the body, or there is something inherently wrong with the knee, the individual usually outgrows the problem," Dr. Adams said. He worries more about the "competitive middle-aged American who doesn't know the meaning of modeeration and exceeds his ability to exercise."

Bill Rosen, 55, an administrator for the National Science Foundation, is the first to admit "I overuse my knees" - he takes pride that he's always played "lots of tennis and squash and runs several times a year." But Rosen's activities came to a halt last January when his knees began to "hurt like hell." Puzzled, since he had never suffered any injury to his knees, Rosen stopped running for a couple of weeks.

After adding a support to his shoes, he resumed his full athletic schedule. Today, Rosen speaks of the "twinges of pain now and then in his knees," but refuses to stop his heavy sports regimen.

Rosen's administrative position does not permit exercising while on the job."As a consequence," he sighs, "I really should lose about 10 pounds. But I am in fairly good shape."

According to Dr. Robert P. Nirshl, an Arlington orthopedist, who is also chairman of the committee on medical aspects of sports for the medical society of Virginia, any excess of weight causes "the pressure put against the knees to be tremendous." Reducing the physical overload on the knees of a middle-aged person is made more difficult by the fact that "the mindset of a 20-year-old college jock does not change when that same individual turns 40."

"The only difference," Nirschl notes, "is that this 40-year-old man now sits at a desk five days a week and is 20 pounds heavier."

Chuck Wolfrum, not quite 30, recently lost 50 pounds. He pursued many athletic activities while in college and after graduating took an accounting job with PEPCO. The desk job soon added poundage, but Wolfrum continued to play basketball every night at a recreation center. Then one evening his right knee acted up.

"I jumped up and when I came down, something just popped."

He couldn't walk for about a week, but after some bed rest, Wolfrum resumed basketball and suffered with his sore knees which continued to "make weird creaks."

Now, 50 pounds lighter, he plays racquetball or basketball every day and has embarked on an intensive program of gradually building up his knee muscles.

Such general conditioning, Dr. Adams maintains, combined with special attention to the specific sport, such as elongating one's muscles for running, are absolute requisites for the recreational or weekend athlete. John Spassoff, director of the Watergate Health Club, recommends preliminary training even for jogging.

"Only after a gradual building up of the muscles and respiratory system should the individual attempt any extensive jogging routine," he said.

Tennis buffs should strive toward making their muscles short and contracted before skipping onto the court, since the sport involves much stopping and starting.

The surface of the courts can also make all the difference in the amount of pressure exerted on the knees. On clay, the player can slide more easily than on cement courts, and is able to decelerate, thus reducing the pressure on his knees.

Regardless of what precipitates the knee problem, the discomfort that results is usually painful and debilitating.

Most orthopedists reluctantly admit that the physiology behind most knee ailments remains obscure and that more research is needed. And when asked how the individual could console himself in times of pain, they seemed just as vague. Aspirin, moist heat, whirlpools and "anything that feels good" were put forward as treatments.

In an MIT report on problems of the kneecap, the researchers concluded that they still knew too little to give advice on avoiding knee trouble beyond "staying healthy and skinny, keeping your muscles well-developed, wearing spongy shoes and avoiding being banged around too much."$

Simplistic, perhaps, but if nothing is intrinsically wrong with the knees, prevention is still the best medicine.