IT IS A BELIEF of people like me, people who condemn hunters and have tried at least once to read James Joyce, that prize fighting is a bad thing. We are against it, feel it is cruel and inhuman, and that it is, in the end, nothing more than one person hitting another until one of them falls down dead or unconsicious. Either way, it is scored as a win.

By and large I hold this position, leaving an asterisk for one Muhammad Ali. He is the one big exception to the rule, the one piece of pure delight in a sport that is otherwise occupied with bashing of brains for three minute intervals and the incessant chatter of Howard Cosell. Ali prances among all this junk like a ballet dancer, never quite stepping into the muck that is the sport of one man beating up another.

This because Muhammad Ali is only incidentally in the business of fighting other men. Most of his life he has either been fighting bigotry or for his own independence or for his own ideas. Now, in announcing his intention to seek the heavyweight crown for the fourth time, he is fighting something else. To call it the clock or age is to simple because that is something we all fight. He is fighting something bigger than that. He is literally fighting for old times' sake.

There is a sense a person has of himself -- of what he should look like and what he should feel like. With Ali, this sense has to be particularly keen because a fighter, more than most people, must know his body. He must know what it can do and what it cannot do, where it is and where it is not. He lives and the tiny world of the fight ring and he wins or loses sometimes by inches -- the difference between a punch that lands and one that does not. A fighter has his body and nothing more. He is born with the basic tools of his trade.

With Ali, the body has gone to fat. He is heavy and paunchy. There is a picture of him, taken about a year ago, in which his stomach is hanging over his shorts so that you cannot read that large Everlast label on the waistband. h

It was a shocking picture, but it was reassuring in a way, too. I looked and I thought, "Et tu, Ali." It is nice to know that even God's best bodies will turn to fat with age and time.

You can fight it. You can keep slim, but if you are like Ali -- like me, if you have not already guessed -- it is not easy. It's hard to turn away the bread and the butter, the sweets and the good, red meat. It hurts to say no to beer and wine, to creamy cheeses and to the fine things that go with them, and at night before bed, to settle for water and a carrot when the refrigerator is stacked with the bounty of this opulent land.

Every day it is a fight, and the only way to win is to pick a bigger one -- have a goal. Without one, you get fatter and fatter and the body that was once so terrific, so responsive, seems weird and all wrong. It bumps into things and pushes against clothes and comes off the chair slower. You encounter it where you should not; you feel it with you, hanging on, not responding, a dead weight leadening your step.

So you pick a goal. For me, it was once women -- looking good for women -- and then later it was health, and now, when I attempt it, it is simply doing it -- if I can get back into shape. When I try to, I run and imagine hearing the music from "Rocky."

But Ali already is Rocky. He cannot merely imagine a fight; he has to have one. And so he shall. He will fight (probably in June) a man much younger than he is. Ali says he can lose three pounds a week and shed something like 25 pounds before the fight. Always, you see, the emphasis is on losing weight. A fighter cannot fight if he's fat.

Some people say Ali will fight again for the money (a $7 million gurantee) or the glory of becoming the first man to win the title for the fourth time. It is none of that. Everyone who has ever stared a piece of bread in the face -- and then succumbed -- knows that the reason a 38-year-old man fights is neither money nor glory nor fame. The reason is fat.