Aaron Pryor will get his biggest payday Friday night, but it would be hard to tell it by his demeanor.

He's relinquished the gold tooth he used to wear. It's been replaced by a plain plastic cap.

Gone are his flashy clothes and, in recent days, gone too are the wild bursts of emotion that built his reputation as, in promoter Bob Arum's description, "the last angry man."

At 27, Pryor says he's grown up. "I'm wearing business suits," he said last week. "You can't wear cowboy hats forever."

Friday night the revised Pryor will defend his World Boxing Association junior welterweight title against lightweight champion Alexis Arguello, who is seeking to become the first fighter in history to win titles in four weight divisions.

The match starts at 10:20 in the Orange Bowl, where a crowd in excess of 20,000 is expected. The fight will be broadcast live on HBO cable network and at about 100 closed-circuit outlets, including the Capital Centre, where the broadcast will follow the Washington Bullets' basketball game. The broadcast starts at 9 with a bout between lightweights Howard Davis and Claude Noel.

Promoters used to grind their teeth the week before a Pryor fight. That includes Arum, who backed Pryor's last bout against Akio Kameda. That was the fight in which Pryor was knocked down in the first round, leaped to his feet and did a standing flip, then waded back in to pound at the tall Japanese left-hander before the mandatory eight-count was half done.

For 10 days before that fight Pryor was teetering on an angry edge, making outlandish demands and alienating himself from the world, said Arum. He was building a rage that finally exploded in the ring.

This time, no problem.

"My angry days are over," Pryor said. "I'm going to beat Arguello by skill, not anger."

Pryor will make $1.6 million for this fight, which is $100,000 more than Arguello's guarantee. That the difference is small, considering it's Pryor's title on the line, has not rankled the fighter. Nor has much else lately.

Today there was a minor battle over the selection of a South African, Stanley Christodoulou, as referee. Pryor objected to an official from a nation that condones racial separatism and initially threatened to refuse to fight. Later he backed down and issued a statement saying, "I am very unhappy to know what happens in South Africa, but I accept Christodoulou as the referee."

Nor have sparks flown between the two fighters. At a press conference for both men Wednesday, Pryor was practically deferential to Arguello.

Pryor's handlers are used to seeing him more volatile. "The heat's always up on the champ," said an assistant at a workout last week. Added Willie Davis, the trainer who has been with Pryor since the boxer was 14, "He likes noise. He's like a chained animal" before a fight.

But after that workout Pryor, who has been characterized in the press more than once as plain "crazy," sat with two newspapermen for half an hour and explained in calm terms his ambitions and intentions in the Arguello fight.

Afterward, one told Pryor, "I thought you were crazy."

Pryor grabbed the man by the neck, growled and said, "I am."

But he was smiling.

Arum said security for Friday's fight has been beefed up against the possibility of angry exchanges between Cuban-American fight fans and some 2,000 Arguello partisans who have flown in from his native Nicaragua.

"We're not concerned about the Latins getting rowdy if Pryor wins, or normal fan fights," said Arum. "But we are concerned with the Nicaraguan political situation." The government in that country is leftist and Arum is worried that could spark enmity among conservative Cuban-Americans.

While it was rainy and windy in Miami today, the forecast was for better weather Friday. The ring at the Orange Bowl is protected by a canopy and Arum said "barring a hurricane, the fight will go on."

Pryor, the product of a raw upbringing in the Cincinnati ghetto, thinks it will be a watershed bout for his career. He said last week, "This fight will make me or break me, even though it's my sixth title defense. The boxing world has never given me recognition as a class champion, even though I am undefeated (31-0) and I have the best knockout record (29). This is the first time I'm getting a proper paycheck."

By keeping his cool and beating the classy Arguello, who is the 2-to-1 favorite according to the Las Vegas betting line, Pryor feels he could change his image.

"I used to be cocky, confident and crazy," he said. "Now I'm for sure and on time."