Up the street, Bobby Berosini and his Dancing Orangutans are on the marquee, Don King's teased hair glows like a halo before the camera lights, and all over town the slot machines are making their seductive little kerchinking noises. Alone in the midst of the prefight glitz is this Brooks Brothers boxer, Michael Spinks.

At training sessions, Spinks wears a conservative plain white T-shirt and gray shorts. If he had a letter sweater he'd turn it inside out. He keeps his trophies, the ones he hasn't lost, in a closet, along with his world heavyweight championship belt, which he treats like some old school tie. "I can reach it if I need it," he shrugs.

There is something incongrously self-deprecating about this carefully groomed 29-year-old from St. Louis, who carries his championship so cavalierly. As little commotion as possible, if you please. It's all so garish, you see, so very undignified.

"I am a boxer, not a fighter," he said. "Give me that respect. I don't fight, I box. Fighting has an ugly sound."

Spinks meets Larry Holmes Saturday night in defense of his International Boxing Federation world heavyweight title, and frankly, he is a shockingly unlikely champion, quite aside from the fact that he is in reality a light heavyweight. Precisely, the first light heavyweight ever to claim the heavyweight title, which he did in September with the historic upset of Holmes by decision.

When the two meet in their rematch at the Hilton Center, Spinks has a chance to accomplish several things. Foremost, a victory would assure him of a position as one of the more historically notable fighters, the first light heavyweight not only to win the title but to keep it.

In addition, Spinks has a chance to become a memorable champion if only because he is appealingly peculiar. He can bring some needed glamor back to the heavyweight division, for he is an articulate, eminently likable champion. After seven years of the workmanlike and frequently churlish Holmes, Spinks seems undeniably debonair, a figure who couples his stylishness with a frequently amusing modesty about the fight profession.

Last weekend, Spinks was watching Jack Nicklaus win the Masters at age 46, which made him think of Holmes, who will be trying to win the world heavyweight title at 36. Then this thought crossed his mind: "Nicklaus wouldn't have lasted if that little ball hit him in the head every time."

"There is no pride involved in losing," he added. "I've been beaten. It's the punishment. The fact is, you come out all banged up, and you can't think straight."

Contrast that to Holmes, who broke his six-week silence today to proclaim during his sparring session: "I've earned and deserved everything I've gotten in boxing. I'm the greatest thing since boxing was invented. I don't have any sympathy for Michael Spinks. This is war, this is like President Reagan the other day with Libya. I'm going to destroy Michael Spinks."

Spinks' September title won't be truly legitimate in some eyes until he has defended it. His original task, becoming the first light heavy to win the championship, has become more complicated. First, can he train consistently as a heavyweight? Next, can he defend his title against a challenger who is so mad, as Spinks put it, "He's liable to try and kick me."

To many, Spinks still does not look capable. He has a rather handsome head, and a narrow Scarlett O'Hara waist that makes people call him Slim. He tapers off to a pair of once-thin legs that caused him to be self-conscious, so he wore long pants most of the time.

Spinks' neat appearance caused Holmes to make some predictable remarks last September about him being sort of, well, effete. But Spinks has gotten these new legs, which have grown considerably thicker since he stripped Holmes of the world heavyweight title, so that now he figures he can wear shorts. Spinks will probably weigh in somewhere between 199 and 203. The 25 pounds he put on for the September fight he claims have settled comfortably, mostly in those legs. Although some speculate that could cause him to lose some swiftness, he claims it suits him.

However, although Spinks may have grown to look more the part, whether he can learn to fight like a heavyweight depends entirely on whom you talk to. According to the Holmes' camp, Spinks never really fought in September. His bout consisted of keeping away from Holmes, then closing in for a few wild flurries. Holmes, meanwhile, appeared to have his arms pinned to his sides.

That could be the primary difference Saturday. Holmes' camp says he has finally gotten his arms up. No matter what Spinks' shape or weight, they claim, he won't withstand Holmes' power. Holmes has sent a message: he will win in seven.

Spinks, however, has a different version of the September fight: He chose his style carefully, studying Holmes on tape even as late as in the locker room just before the fight. It is not hard to buy his story that he is simply a smart fighter, although he may never be called a correct one, considering his unorthodox style in the ring.

"I timed him," Spinks said. "I was setting him up. I was watching tapes of his other fights in the locker room and suddenly I knew how to get through those defenses. It didn't happen until right before the fight, but I knew all along I'd find some way."

Just as he keeps his trophies hidden, Spinks is not one who is easily caught up in the prefight babble. That may have been his biggest asset in September, when there was perhaps more than the usual amount of talk.

What with Holmes seeking to tie Rocky Marciano's 49-0 mark, and with Spinks seeking his landmark victory, there were lots of unkind words flying around. Most of them came from Holmes, and although they seemed to roll off Spinks at the time, he says now that he was uncomfortable. "I thought, 'Let's keep it classy, Larry,' " he said. Some animosity was bred, and according to Spinks, he used it to his advantage.

"Larry was having a great time," Spinks said. "Nobody could tell him anything at all. I didn't taunt him, I didn't say anything at all, and the whole town knew it. He said everything to me. He tried to strip me of everything. He talked about my brother, my family, my mother. He tried to tear me down.

"Then I just gracefully beat him. I took his championship and went on about my business."