Pinball used to be more of a sinner's game, played in taverns. You'd go in, have a few drinks and then find yourself standing before the glowing pin-ball machine in back. (It was always in back, it seemed.) You could set your drink on a sheet of glass that protected bumpers and flippers, miniature gates and other assorted gizmos that lit, sunk, dinged and bonged when kissed by that small steel ball.

In went the coin: What was it, a dime back then? You snapped the plunger and that sent the ball rattling up the chute on the right-hand side.

You were pitched slightly forward almost at arm's length and your sweating hands gripped the nearest two corners of the glass-and-wood devil. And then you shook it in short, jabbing pumps, trying to keep the ball high up in the "playing field."

No sound was sweeter than the ka-chunk, ka-chunk of your score registering on the back glass, but you didn't dare look at the rolling numbers for fear of losing a beat. And you didn't dare rock the machine to hard for fear of tilting it, at which point the game would end and you'd have nothing.

Ka-chunk ka-chunk. It was heaven.

That was then, and now is now - pinball has joined the real world. It's still in taverns but not as much as before, for now there are the so-called video electronic games to take your money. So pinball is trying to make it on the outside in shopping centers and such. The game is computerized and digitalized, and scores no longer ka-chunk, ka-chunk so much as beep-beep. And because the game has gone more public, more kids are playing it, as they did here Saturday in something called the First National Pinball Tournament.

Twenty competitors made it to the finals in the ballroom of the Playboy Towers hotel, most of them youngsters who couldn't get served in a bar. The average age was 19; the youngest contestants were boys aged 11 and 12.

"Just settle down, take it easy, relax now," admonished Lila Cohen, mother of 11-year-old Jeff Cohen. That was during the first found and settle down he did: He reached the finals by shooting a whopping score of 765,790 for five balls on Bally-s Mata Hari machine. He got a lot of those points on his last ball, using all the body English his small body could muster. Those flippers fairly sang.

"Yeah, it always happens this way in the tournaments," he said after his performance. "I always come through on the last ball." But, alas, young Jeff finished fourth in the final field of five. He was only 31,441 points from third place and winning a Datsun, which the top three finishers received. The winner was Ken Lunceford, an elderly 19, from Columbus, Ga., who took time out between rounds to call his buddies in a hometown arcade for encouragement.

Contestants competed on machines that stood on an illuminated disco dance floor; chains cordoned off the players from the publis. Playboy bunnies ran scores from the floor to the scorers' desk where the totals were projected on a back screen.

There were no tickets to the event and no entry fees. The purpose was not to make money but rather, in the words of Tom Nieman, Bally's promotional sales manager, "to give the event as a "whitwash or image-polishing attempt.

"We know we're under a light all the time and we have to do exactly what the law says."

Commercialism hung heavy over the tournament. The balconies were bannered with the names of sponsoring companies and the smell of business was everywhere. Datsun gave away cars, and even had a model parked near the playing floor.Faded Glory, a clothing manufacturer, outfitted all the contestants in flashy colored pants and jackets. Playboy put the contestants in Playboy T-shirts. And the Bally Manufacturing Corp. not only furnished its machines for the contest, but gave one - worth about $1,600 retail - to the winner, Lunceford.

Whether this was a national tournament at all was another question. The 20 finalists - 19 males and one female - emerged from a starting field of a reported 62,000; even so, the competition was limited. To compete, you had to sign up and play at one of a chain of suburban entertainment centers and work your way toward the final 20 from there. Not so coincidentally, the chain is a wholly-owned subsidiary of Bally, the pinball manufacturer.

Rules for contestants were strick. For one thing, they were not allowed to smoke while they competed. This did not meet with the overwhelming approval of some players, such as Glen Buck , 19, of Abilene, Tex., who said, "I may not like to pick up a cigarette but maybe one time if I'm playing, But I like to know it's there. Like if I'm having a bad game, to relax I'll just pick up that cigarette and take myself of couple of drags." For the record, Nicotine Glen didn't make the final five.

And God forbid that one of the younger players should be photographed with a bunny. This warning came straight from Allan T. Zachary, Bally's public relations man. Something to do with image, presumably. The bunnies, however, did not exactly look like vamps. They had on black body suits with turtleneck collars and short beige skirts sashed around their waists. They wore bunny ears, of course, in color-coordinated black.

Said one miffed bunny: "One of those PR guys - I don't know who it was - told us about corrupting kids - what about pinball machines, period? They weren't even allowed in Chicago until a year and a half ago. Come on."