Name: Nelson Vails.

Home: Zoo York, Zoo York.

Occupation: Sprint cyclist, budding star.

Have a look at Nelson Vails, a 21-year-old bicycle racer who is faster than a speeding taxi and stronger than the Harlem neighborhood he escaped. To his friends, and that includes you, stranger, he is Cheetah--the fastest cat in the jungle. To his sport, he is just the kind of brash-talking, crowd-pleasing personality needed in the big time.

"I'm one of a kind, if I can say that about myself," says Vails, who isn't talking about being the only black among this country's sprinting elite. Vails is talking charisma. He plays to a crowd like an actor to an audience. His enthusiasm is all the more appealing because it seems genuine.

"This sport needs more riders like Nelson," says Tracy Lea, an Easton, Md., cyclist here for the National Sports Festival. "He's so handsome and such a warm person, he can get a crowd up and cheering."

There may not be another athlete among the 2,600 here for the nine-day U.S. Olympic Committee sports festival who has come as far, and gotten here as fast, as Vails. A few years ago he was dodging traffic and jumping potholes in New York City as a bicycle messenger. Now he is one of the top five competitors in the country.

"He came along so quickly it was phenomenal," says Les Barczewski, who raced 12 years before becoming the national sprint champion only to look back and see this rookie riding his wheel and blowing steam. "He's still inexperienced, but he's very fast. And that makes him very dangerous."

Cycling was among the first events on the first full day of competition at the festival. That seemed appropriate in this state that is as bicycle-conscious as any in the country. Indiana is home to a half-dozen past and present cycling champions and it was the setting for the movie "Breaking Away," which celebrated cycling as metaphor. No one here can quite remember for what.

Still, the cyclists chasing each other in steep circles in a just-completed outdoor velodrome were competing with a few thousand other athletes in a dozen sports for the attention of fans.

"There are so many different sports being played at the same time in so many different places, it's really kind of good and terrible at the same time," said Bernard Kauffman, a 38-year-old electrical engineer on vacation from Chicago, who passed up cycling, field hockey, tennis and half a dozen other sports to spend his morning watching a 50-kilometer walk. "Don't ask me why I picked this one. I was just curious."

With 149 events being contested at 18 locations, the competition for spectators will be as interesting as some of the games being played. Each of the sports has a publicity liaison assigned to it and they have already begun touting personalities to the media.

How about a Polish defector in the modern pentathalon? Slavek Rotkiewicz, a member of the 1976 Polish Olympic team who defected while competing in Texas three years ago, is here. A naturalized American, Rotkiewicz, these days known as Steve Rhodes, hopes to compete for the United States in the 1984 Olympics.

There are enough brother, sister, father, son and daughter combinations competing here--with and against one another--to keep "Family Feud" in contestants for years.

Last year at the sports festival in Syracuse, N.Y., two of the most popular competitors were an 11-year-old rower whose mother made him miss a press conference to take his nap and a 78-year-old archer from North Carolina who competed from a wheelchair. The youngest contestant this year is an 11-year-old girl from Oklahoma entered in a sport called rhythmic gymnastics and the oldest a 64-year-old skeet-shooting woman from Florida.

Vails has been an early standout. With his modest Rastafarian curls and his fast-talking manner, he has drawn attention to himself and his sport.

"I like to make people happy. And I like to talk trash," said Vails after Friday's opening parade through downtown Indianapolis, where he provoked the crowd by yelling "Who's your buddy?" and "Who's from Zoo York?"

"You can't help but love the guy," says Barczewski who admits that before he met Vails "I was prejudiced against black people. He showed me how wrong I was." The two cyclists, the champion and the challenger, now room together on the road.

Barczewski has ridden his cycling talent around the world. He has competed in Europe, the Caribbean and New Zealand. Vails has ridden his way to Las Vegas, Pennsylvania and California. They have been exotic enough.

"I have been to Disneyland," says Vails. "Who would have thought?"