It seems so safe, this Nintendo craze. Kids glued to television sets save the world in the crime-free comfort of their own suburban homes. No small game pieces for tots to swallow. No asphalt to fall on. No tackling.

The main fear spreading among parents is atrophy of the brain.But now comes a doctor who contends America's youths are susceptible to an outbreak of "Nintendinitis," a condition that's a grandchild of the dreaded tennis elbow, a cousin once-removed from carpal tunnel syndrome.

"In a way, it's sort of a mini-tennis elbow of the hand," said Dr. James Casanova, an internist and assistant professor at the Medical College of Wisconsin in Milwaukee.

As Casanova explains it, rapid manipulation of the computer game's control buttons can cause inflammation in the flexor pollicis longus, the tendon that allows thumb movement.

Computer gameitis isn't new. A Salt Lake hand surgeon, Dr. Doug Hutchinson, remembers other versions, such as "Pac Man-itis" and "Pac-man wrist." But Hutchinson said he hasn't seen any local cases. Nationally, two cases have been reported in medical journals.

"It's rare and it's easily treated," said Hutchinson, an assistant professor of orthopedic surgery at the University of Utah Medical School. "It gets better if you stop doing it. It doesn't take a medical degree to figure that out."

Hutchinson advises youths who suffer from the condition to switch hands. Casanova prescribes several aspirin and a few days' rest. Despite the low numbers of cases reported, Casanova thinks an epidemic is possible, thanks to the computer game that is as standard in many American homes as indoor plumbing.

"There's probably an epidemic in this, we figure," Casanova said. "But the good news is it's not a serious problem. We didn't think this is too profound, but it is entertaining."

Casanova and his wife, Jean, of the hospital's Hand Rehabilitation Clinic, published a letter identifying the condition in the January 1991 issue of the Journal of Hand Surgery. Another letter mentioning the syndrome was published in the New England Journal of Medicine.

Casanova named the condition after examining an 8-eight-year-old boy who reported a sore right thumb. The doctor pinpointed the problem when he learned his young patient received a Nintendo set for Christmas.

But Jeff Hansen, 11, doesn't complain of any sore thumbs. The Nin-tendo champion of the world, who lives in Murray, has played computer games since he was 3, and Nintendo since he was 9. The fifth-grader won a $10,000 savings bond and a convertible on the way to claiming his title last year.

His mother, Karen Hansen, says he doesn't play as much as other kids in the neighborhood. "He was born with it. He came out and said `Give me a paddle.' "

Jeff Hansen logs about an hour of Nintendo action a day, three hours when he has a new game to play. Yet due to a recent knee injury, his mother worries more about his participation in contact sports. "Boy, it's more dangerous for him to play football than Nintendo."