IT WAS THE WORST KEPT SECRET since George Shultz's tiger tattoo, and nearly as embarrassing. Sugar Ray Leonard announced several months ago that - surprise! - he is coming out of retirement to become the first boxer in history to rule in five separate weight classes.

Apparently he isn't as content as he thought.

This time the date is next Monday and the opponent is a light heavyweight champion nobody knows named Donny Lalonde.

So it is true. Behind the doe eyes and cherub face, behind the trappings of family and sensibility, Sugar Ray Leonard is something as common as a glass of water: another fighter who couldn't quit.

Sugar put down his gloves for the first time in 1982 when an eye injury threatened. Two years later he un-retired to fight Kevin Howard, but after a disappointing showing, he quit again. Then after coming back to dispose of Marvin Hagler in 1987 he retired yet again.

And now this.

It has been a storybook life. Sugar Ray the Olympic gold medalists. Sugar Ray the world champ. Sugar Ray the $40 million man. Sugar Ray the multi-media mega-star. Sugar Ray the father who quit at the pleadings of his wife and children. The man with the class to call it a career.

Then came the chance to fight Marvin Hagler and he was back, his eyes filled with ego. "I'm doing it because everybody said I couldn't," said Leonard. "I'm doing it for myself."

He certainly was.

What matters is that Sugar Ray Leonard was right in choosing health over more wealth, and if I am to say anything further about him, it won't involve grousing. I will, rather, simply hope he never changes his mind. - Chicago columnist John Schulian, 1982.

He did change his mind, though. And since Marvin Hagler didn't put out his delicate eye - one doctors said he could damage permanently if he continued fighting - he's going to try to cheat fate again. Eyes are one thing. Glory is another. Sugar Ray Leonard isn't going to back down from anyone, including his doctor.

It isn't just what Leonard could do to himself by continuing to fight. It's what he's taught us. We can see that health and wealth and family and common sense aren't as important as cold ego. He has taught millions of kids that risking the future is worth it if you like the present enough. He has joined Louis and Ali and Duran and all the rest in showing how boxing will hook a fighter with its addictive charms and no matter how much money he makes, and no matter how clean the break, he'll be back for a fix one day.

There hasn't been a rehab center built that can stop a boxing addict from returning to his fate.

"It's the adulation society provides, and even if the fighter loses, it's worth it. He's in the limelight again and again and again," says noted University of Utah sports psychologist Dr. Keith Henschen.

"A boxer gets recognition when he retires and another shot of adrenalin when he comes back. Then he gets a third shot after the fight whether he wins or loses. And if he wins he can just keep on going."

Everyone knows he can come back. We know he can beat up Tommy Hearns and Marvin Hagler and probably Donny Lalonde. He might even work his way up to a fight with Mike Tyson. He can eat in his elegant restaurants and smile his charming smile for the cameras. But he can't show us he has class. Behind the tuxedos and diamond rings there lurks just another common boxer who didn't quit when he had a chance to make an impact for good.

He was supposed to be different. But for all his style and grace, we've seen his kind before.