THE JOGGING fad peaked in early 1980, and running analysts predict it will be all downhill for 1981. This does not mean that the hard-line jogger, who cannot be rehabilitated, will give up the sport. But the person who tried it for kicks and because everyone else was doing it has finally come in from the cold and has gone back to doing pushups in his bedroom.

No one knows why jogging fell off. Some believe when President Carter stumbled in a race last year, it was the beginning of the end for amateur runners. Others theorize that many people discovered you never got to talk to anyone when you were jogging after work, and you could meet a much better class of people in a warm singles bar.

I date the beginning of the end for jogging to last summer when I went to see Guggenheim and found him in his garage.

"How about a five-mile run to the Pentagon this morning?" I asked.

"I can't," he said. "I'm working on something that could make me rich."

"What is it?"

He showed me a round piece of wood. "I call it a wheel."

"What good is it?"

"It's no good by itself. But when I attach it to another wheel with this crossbar, and connect it to these other two wheels in the back and put this seat on top and an engine here to turn the wheels, a person won't have to jog any more."

"You're a dreamer, Guggenheim. Who would want to ride when he could run instead?"

"Don't you see, man? This invention will free millions of joggers from having to use their own legs. They can cover twice as much territory in half the time. They won't have to worry any more about aches and paines in their bodies -- they won't even have to breathe heavily. They can just sit there and enjoy the view. The wheel will take the pain out of jogging."

"But I thought pain was part of jogging. I was under the impression people jogged because it hurt all over."

"Some do, but there are millions of people out there who have low pain thresholds. That's the market I'm going for."

"It sounds great on paper," I admitted. "But if you don't use your own legs how can you call it jogging?"

"You can still wear your sweat suit and running shoes. You can do everything a jogger does, except move under your own power. The thing that's going to sell this is that you don't perspire. You can do 26 miles and not have to take a shower."

"I forgot about that. Are you looking for investors?"

"I might be when I go into mass production. But at the moment, I'd like to stand on my own two feet."

I took one more look at Guggenheim's crude machine and realized I was gazing into the future. I always knew that someday man's genius would lick the jogging problem once and for all. But I never thought it would come so soon.