Shuffleboard can involve a surprising amount of exercise, especially when, like Carleton Kenneth Lewis, you have to keep walking to the other end of the court to see exactly how far you have put your opponent in the hole.

"Oh my," Lewis said after he had gone to inspect one of his more than ordinarily spectacular shots on his backyard court in Annandale. "Now you have two in the kitchen, with blocks on both of them, and one in the grass. Oh my."

He strode back to the starting line and peered down through Coke-bottle-bottom lenses at his fourth and final disc. "I think I'll have to put one in the 10 triangle to give you something else to worry about," he said genially, and proceeded to do so.

"Now remember," he said to his opponent - who was trying to salvage a shred of dignity from a potential 45-point loss in a 50-point game - "aim your cue like it was a rifle, and keep you head down. It's like golf, lifting your head ruins everything."

His opponent, who had already had enough to worry about, now was treated to a series of mental images of the lifted-head golf shots that had led him to give up that game. Not surprisingly, he blew the shot.

"Oh my," Lewis said as the disc slid off the concrete alley. "Shall we play another game, or would you like to take a break?"

"What are you doing to him, Carl?" asked Mabel Lewis, his wife of nearly 60 years. But she knew. Her husband was winning again. It's the only way he knows to play, whether the game is shuffleboard or life's little problems, such as how do you make it across the Little River Turnpike to the supermarket when the cars are going 60 miles an hour and you're 85 years old.

"What I do, you see, is chain the bike (an English three-speed) to a post and then look ahead for a break between the cars. I can't see very well anymore and I can't run very fast, really, so I have to get started before the opening actually arrives. If I make it to the middle I do the same thing again."

He uses the bike instead of his Pontiac "because it saves wear and tear on the fenders, don't you know." He learned on his cue and considered. "There are two classes of pedestrians in Fairfax County: the quick and the dead."

There are social services for the elderly in Fairfax County which include such things as grocery hauling and grasscutting, but Lewis would druther pass. He has two sons, four grandsons, two great-grandsons and finally, joyfully, seven great-granddaughters, some of whom live close enough to help out.

The Lewises do accept the Meals on Wheels service, because it is a great convenience for a pair of people who eat as sparingly as fashion models.

Otherwise they are part of the solution, not the problem. Lewis spends much of his time badgering county officials and civic groups about sporting programs. He delights in teaching swimming and ice skating and canoeing and bowling to young people, but his deepest concern is sports for old people, because he recognizes the possibility that he may be one some day.

"Shuffleboard is a great game for old people because it does not take speed or strength, he said. "But it is a game of strategy, skill and control, a far from simple game, and it is just as great for young people. The best part of it is that old any young can play together on fair terms."

(Unless they're playing Lewis, who was delivering this pitch while casually destroying his opponent across a gap of half a century.)

Lewis has honed and refined his shuffleboard spiel through years of letter writing, telephoning and testifying. He is Fairfax County's senior and favorite civic gadfly. "Mr. Lewis is polite, reasonable, logical, factual, knowledgeable and persistent," said Ann Payne of the Fairfax County Park Authority.

"He is also irresistible. It is a privilege to be hounded by Mr. Lewis, because it makes you feel good when you've done what he wants you to do. I wish I were as young as he is."

Lewis was an accomplished do-gooder long before Payne was born. In 1942, for instance (before he went off to his second World War), he was proclaimed Arlington County's leading citizen because of his work on the Arlington Community Hospital project, the county's first. The drive featured, among other things, Mabel Lewis riding around the county in a sound truck saying, "I am the voice of the women of Arlington. We want our children to be born in Virginia."

Lewis has also taken up certain matters with several presidents and the Pope.

So far Lewis's shuffleboard campaign has put a dozen alleys in county parks, and he's just beginning. "My main idea is to get families to build their own courts. You can combine a patio and a shuffleboard court, for instance; call the Portland Cement Association in Arlington and they'll send you a free booklet that tells how.

"And there are plenty of shufleboards at motels and resorts that can't be used because the equipment gets torn up. Boys use the cues for spears or bats and the discs get lost. But you can buy a family set with telescoping cues that fits in a corner of the trunk and use it anywhere. It costs about $30, less than one good tennis racket, and it will last almost indefinitely."

The Lewis backyard court was built by his family and a group of people from his church, and is in almost constant use during what amounts to a continual open house. When he pedals over to Mason District Park to see if there are any old folks who need bucking up he soon is surrounded by children who want to play with him.

"Tell you how crazy I am about children," he said "or maybe just how crazy I am, after I retired (as chief of the U.S. Tariff Commission's agricultural division) I took up teaching high school."

Lewis takes his shuffleboard show on the road from time to time, to such places as Capon Springs, W. Va., where he is addressed as "Mr. Shuffleboard;" Barbados in the Netherlands West Indies, where he singlehandedly revived interest in the game; and St. Petersburg, Fla., shuffleboard-and-park-bench capital of the world, where he declines to compete in organized tournaments, preferring to defeat the seniors champions privately.

After lunch, during which Mabel Lewis pressed half her tunafish sandwitch, a double handful of her granddaughter's cookies and a bag of apples on the visitor, there was a final game. "Think positively," Lewis abjured. "Stop talking about the shot you missed and think about the one that's going to work."

His pupil fell behind at first and then began to overtake Lewis. The younger man suspected Lewis was throwing the game, but could not pinpoint how. "My, my," Lewis said innocently at the end, "you seem to have won.

"Now, you come on back, and bring the family. I'll teach the children shuffleboard, and then while they're playing I'll straighten out your golf game."