Hemingway wrote that happy men are the bravest men. Such is Alexis Arguello -- happy and brave and a fine boxing man.

Like most fighters, he saves exercise for the end of his workouts. After the shadow boxing, the sparring, the heavy bag, the speed bag, the heavy bag again, he climbs into the ring, where a clean, white towel has been laid.

He does his situps rapid-fire; first straight-legged, then bent-legged, then one-legged with one foot tucked behind a knee.

In an hour and a half of hard work, he has uttered not a word to the 50 or so fans who have gathered to watch him a week before the most important fight of his career.

Now Arguello lies on his back and lifts his legs over him until his toes rest on the canvas beyond his head. The back-stretching exercise leaves Arguello staring at his own shorts, soaked from perspiration and water he has poured over himself.

Droplets run along his sleek body, gather on the shorts and fall: drip, drip. Arguello's dark eyes light merrily. He extends his tongue and darts his head back and forth, catching the rain like a frog after flies.

Happy and brave, Alexis Arguello welcomes those who admire him. No one screens the people who come to watch him work in the little cinder-block gym at abandoned Tropical Park race track. There is no admission fee. Arguello, who on Friday will try to become the only fighter in history to win four championships in four different weight divisions, only asks that his fans be quiet when he works.

Afterward, he is one of the people, mingling with the men who speak Spanish, laughing, staying until no one else wants to talk with him.

A boy steps up for an autograph. Arguello points to his bare stomach and tells the boy in Spanish to hit it.

The boy extends a hand and pokes at the lightweight champion's washboard stomach with the tips of his fingers. No, no, says Arguello, hit me. Hard.

The boy smiles at the schoolyard game. He balls his fist and whacks Arguello. "Nada," says the boxer with a laugh. The boy strikes again. "Nada."

The men laugh and Arguello ruffles the boy's hair and pinches his happy cheek. He takes the paper and writes: "Para Lupe, con todo respecto, Alexis Arguello." He dots the "i" with a Roman numeral III, to signify his three crowns.

Friday in the Orange Bowl, Arguello will fight Aaron Pryor for the World Boxing Association's junior welterweight title. Arguello is lightweight champion; he has been featherweight and junior lightweight champion. Only five other fighters in history have held three titles in different weight classes. The last one to try for four was Henry Armstrong, 40 years ago. He failed.

Many believe Arguello is the finest ring technician of modern times. He is smart, powerful for his size and, above all, graceful, and he has the fighter's heart that knows not how to quit.

He has never shared the adulation accorded a Sugar Ray Leonard or Muhammad Ali, but he has done well. Friday's fight will bring him $1.5 million.

Still, Arguello remembers lessons of poverty he learned in his native Nicaragua and he clings to notions of morality that do not fit snugly with millionaires.

He would rather have been a doctor or engineer, said Arguello, but when he was 14 and times were lean for his family of 10, he discovered that fate had given him the ability to fight. The first to recognize that ability was a brother-in-law, "but he was a bad example," said Arguello in English. "He was always drinking, fighting in the streets with women."

This brother-in-law lived well. When Arguello was young, the man astonished neighbors in Managua by turning up in a Ford Mustang. "Some car," said Arguello.

Arguello remembers seeing a boy looking through a window of the Mustang, shielding the glare to see all the chrome wonders within. The brother-in-law saw, too, and stormed out of a bar to shoo the child away.

Arguello remembers: "If that was me, you know what I would do? I would say to the boy, 'Come on, you want to go for a ride?' That man, he killed the spirit of the kid."

Nor does Arguello abandon his sophisticated moral code when he fights. Happy and brave, he fights to win. Before and after, he bears no grudge.

Fight fans long will treasure the image of Arguello, after he had dispatched Ray (Boom Boom) Mancini in the 14th round of their title fight, hugging the loser and consoling him in words picked up over television microphones:

"I love your father (Mancini's father was there). It's the beautiful thing you have, like I have my father. Take good care. You are going to be a good promise. I promise if there is anything I can do for you, let me know."

Says Arguello, "In my profession, my job is to concentrate, do my work. Out of the ring, I have to behave like you or anyone else."

He views the notion of fighters as hard, mean people as a misconception. "It doesn't mean you have to offend anyone. It's like with a child; you have to know when to punish them. You can't punish them every day. That would be crazy."

Arguello is a tall, hard man at 138 pounds, two pounds under the junior welterweight limit. He will operate at no size disadvantage. In fact, he is three inches taller than Pryor, whose title he seeks. And with the experience of 80 pro fights against only 31 bouts for Pryor, Arguello is a 2-to-1 betting favorite, according to Las Vegas oddsmakers.

Arguello is excited by the prospect of becoming the first man to win four titles. "Besides a big step for me, in the boxing world it's something no one did. And probably no one will try it for a long time. Nobody tried it for 40 years. It would be a hell of an experience."

He will carry into the ring a well-documented ability to adapt to circumstance. "I have thought since we signed this fight that the left (jab) will be important (in keeping the swarming Pryor away), but if that doesn't work, then what do I do? I try something else," said Arguello.

And he will bring a fighting style that is pure pleasure to watch: perfect balance, patience to wait for an opening and the ability to strike decisively with a cocked right hand when the opening comes.

Win or lose, Arguello at 30 plans to give only another year to boxing. At the end of 1983, he will retire, "I hope," he said, and turned his dark eyes toward the ceiling and clasped his hands in prayer.

A victory could give him one more chance at a truly big fight, this time with Sugar Ray Leonard should the welterweight champion change his mind and decide to box again. How does he view that prospect?

"My father always told me," said Arguello with a smile, " 'Don't sell the meat until you have killed the deer.' "