In the commercial, a black basketball player walks a little stiffly onto a playground court wearing two artificial legs. He misses his first shot, wobbles and falls down, but refuses the proffered hand of another player. Then he makes his next shot and his face radiates satisfaction. The smiles on his teammates' faces are a mixture of incredulity and respect.

Real life rarely mimics the make-believe world of television commercials. In the case of Billy Demby of Landover, it does. He's the man doing the acting, and it's not much of an act.

Demby, 37, came back from Vietnam unable to walk, losing both legs in the flash and fire of an enemy rocket. An avid playground basketball player before he was drafted, by his own account, it was years before he "finally got it together again and did something for myself."

He will do something for himself again on Sunday when he participates in his fifth Marine Corps Marathon as a wheelchair athlete, representing the Achilles Track Club, a Maryland club for disabled athletes. And his commercial for the Du Pont Co. has also served as a reminder that a disability does not necessarily mean the end of the line for a competitive athlete.

Though he cannot use the artificial legs shown in the commercial to run marathons, there is no question they have changed Demby's outlook on life. They have become so much a part of him, he says he doesn't even think there's anything unusual about his accomplishments.

He wears them all the time in every-day life, and they have allowed him to play pickup basketball on the playground, against able-bodied athletes -- something he never thought would be possible.

"Everybody likes to be normal, whatever that means, or as close to that as possible," Demby said yesterday. "By me competing standing up, I'm able to fit in to a certain extent . . . I never had any idea I'd be doing anything like this."

Demby's artificial legs are made of a new plastic known as Delrin, developed in the last two years by Du Pont. Delrin's properties allow the material to bend and stretch without losing its original shape. Researchers in Seattle working with the product recognized the benefits for artificial limbs, which until then had been stiff and unyielding. They developed "the Seattle Foot." Demby wears the Seattle Foot when he walks, exercises and plays basketball.

"With this material they were able to create prostheses with almost lifelike qualities," said Lee Tashjian, Du Pont's director of communications. "If you met Bill on the street wearing long pants you wouldn't have any idea he had two artificial legs. It's incredible when you see him play basketball."

Du Pont's in-house magazine did a story regarding the positive affects Delrin will have for amputee athletes because of its strenth and elasticity. "That's how we originally came up with the idea of doing a commercial," said Tashjian. "We had a choice, we could find an actor here {in Wilmington, Del.} and we decided we probably should not. We wanted to present a real honest to goodness real-life situation and produce it accurately and it would have a greater effectiveness."

After contacting veterans' organizations around the country, Tashjian learned of the U.S. amputee basketball tournament in Memphis last summer. "We decided to find "The marines, from day one, were very receptive to wheelchair racers. They were one of the frontrunners in that respect. Some races even today don't want us."

-- Paul McDowell

one of those guys and show him in a basketball situation to show how well the product works," Tashjian said. "It would demonstrate the product quality extremely well."

It has done exactly that, and the company has received "absolutely outstanding" reaction, according to Tashjian.

Demby, meanwhile, says few people have recognized him from the commercial, and that's fine with him. "It's just something anybody could have done. There's nothing special about me. I'm a regular type guy, trying to compete in a mobile world. But to compete against the next guy, I have to work twice as much or 10 times as hard as the next guy to be accepted."

Demby runs marathons and plays basketball for recreation, but he is a nationally ranked disabled track and field competitor. He holds the national amputee record in the shot put, discus and javelin.

Before Vietnam, Demby played basketball and made Sears batteries in his hometown of Price, Md., with little or no aspirations for anything better. Now, after going back to college for a degree, he counsels other disabled people.

"If it wasn't for this," he said, looking down at his artificial legs, concealed in sweat pants, "I'd probably have continued playing basketball and working at the battery plant. I think sports are an escape for disabled people. If not for sports, I don't think I'd be here today.

"I don't know if it {losing limbs} is something you ever get over. You wake up every morning with those two things against the wall waiting for you to get into. It's an adjustment. You've got your up days and your down days and some days are really low.

"It's a matter of looking at things in a different way. To borrow a phrase from the organization I work for, if I can do this, I can do anything. You see, most disabled people think life is over with, and when you get them involved in sports or recreation it puts them in another frame of mind."

Demby will be one of 12 wheelchair entrants in the marathon from Achilles. Approximately 30 physically handicapped athletes -- some blind and some in wheelchairs -- are expected to complete the 26.2-mile distance.

The blind runners will also be competing in the U.S. Association of Blind Athletes marathon championships. Five-time USABA champion Harry Cordellos is back to defend his title in his ninth Marine Corps Marathon. In addition, the D.C. Special Olympics is hosting the Special Olympics mini-marathon and it will be attended by Special Olympians from across the country.

The Marine Corps Marathon is acknowledged as being a large race receptive to the needs of the average competitor. Since four wheelchair racers, one blind runner and five deaf runners entered the fifth Marine Corps race in 1980, it has also been accorded the same distinction by disabled runners.

"It's a well-organized event," said Paul McDowell, 48, another member of Achilles and one of the four wheelchair participants to race seven years ago. "The marines, from day one, were very receptive to wheelchair racers. They were one of the frontrunners in that respect. Some races even today don't want us. For example, if I were to run at New York, I'd have to start three hours before the main race, at 8 a.m."

The disabled athletes merely want a chance to compete, just like anyone else. They know that sports and the competition it provides offers disabled athletes the same benefits it does able-bodied competitors, but goes one step beyond. It often restores the self-respect and motivation that existed prior to their physical problems.

"I think the competition part is important, especially if you're competitive at an equal level with other, nonhandicapped people," said blind runner Rick Holborow, 24, preparing for his first Marine Corps Marathon. "It's more valuable for me because you are judged on what you can do because of your ability and not with the added phrase, 'He's blind'. If I can compete on an equal level and the handicap is not an issue, it's definitely more satisfying."

Demby concurred.

"If I can compete on this level," he said, "I can compete on any other level -- like going back to school or getting a job."