In the boxing business, it is a recognized truth that everything below the heavyweights is a slow sell. The light heavies diet upward to escape their own miserable class. The public and promoters are indifferent to the good middleweights. The welters and lightweights are left to fight for comparative crumbs. The tiny featherweights and bantams are generally Orientals or Hispanics whose paydays are pegged to their previous standard of living. Boxing's small men are dealt out of boxing's big purses.

Hark, then, to a shining contradiction of most of what has just been said.

He is Sugar Ray Leonard, 147 pounds of welterweight, and a millionaire after only 20 professional fights (20-0). Leonard, whose next fight is Saturday in Las Vegas against Adolfo Viruet, now commands $200,000-plus for stepping into a ring with gloves on. That has been, roughly, the going rate for his last two fights but the price is going up.

He's hot in the marketplace.

He owns no title, has fought none of the topranked welterweights, is sometimes accused of picking his personal safety. Yet the 22-year-old from the Washington suburb of Palmer Park may be boxing's most recognized property after the omnipresent one, Muhammad Ali.

He is the darling of the television networks and at the same time is their creature. They gave him name recognition by televising 13 of his fights, and Leonard hasn't let them down. He has yet to lose and his fame has been cumulative.

Nor does he forget, when time and events permit, to ham it up for his sponsors. His purloined Ali shuffle and his bolo-punch gestures are bare-faced steals. The red, white and blue tassels on his boxing shoes are reminders that he was an American Olympic hero at Montreal in 1976, and his polite introductory bows to all sides of the ring in the continental manner delight the fans.

It also happens that Leonard can fight better than the skeptics thought. He is rated only as the No. 4 challenger but on March 24 at Tucson he made believers of thousands. He proved he was not limited to fast hands and dancing feet, but could punch when he destroyed No. 6-rated Daniel Gonzales with one punch, the first right hand he threw at an opponent who was becoming a menace. End of fight in round one.

Leonard was very pleased by that. He desperately wanted to be known as a complete fighter. "Now they won't keep saying all I got is fast hands and fast feet," Leonard said. He would like to be known as an executioner, too. In his 66 fights, nobody else had even knocked Gonzales off his feet.

This week, Leonard's attorney, Michael Trainer, will be in New York to hold conversations with Jim Jacobs, manager of Puerto Rico's Wilfredo Benitez, holder of the world welterweight title. The match may be arranged for September, after Leonard's contract for four more fights for ABC-TV expires.

"Then we'll throw it out to open bidding by all networks," Trainer said. "All of them are talking Leonard-Benite and I think they are antsy enough to give us what we want." He also indicated there would be no way Leonard would accept less money than the champion, considering that Leonard is the better known fighter.

The boxer, Leonard, is known officially as Sugar Ray Leonard Inc. On Oct. 21, 1976, at a time when his Olympic gold medal represented most of his net worth, he paid a $35 fee to the state of Maryland for incorporation papers. This was done for practical business purposes on advice of counsel Trainer, a Silver Spring attorney. It was the members of the Wildwood Exxon softball team who provided the $21,000 seed money for Leonard's corporation until he could make a payday. Trainer and a friend, Janks Morton, and others had known him as the boy who used to like to watch that team play before he found fame in the Olympics. "Twenty-one fellows put up $1,000 each," Morton said, "Lawyers, store-keepers, gas station owners and other people we knew who had faith in Sugar Ray."

Each got his money back with $40 interest within six months when Leonard got $40,000 from CBS for fighting Bull Vagis in Baltimore in his first bout. Thus Leonard wiped out his corporate debt.

Sugar Ray Leonard Inc. also has set up a penson plan for its president, chairman of the board, and chief executive officer and only employee. No minority stockholders to bug Sugar Ray. He owns all of the 100 shares of stock in his firm. A big chunk of his purses goes immediately into his pension fund. "All Sugar Ray gets for himself now is walking around money," Trainer said.

His net worth has shot up spectacularly. Leonard took more than $200,000 out of his fight with Johnny Gant, in Capital Centre, "and almost a quarter-million" out of his one-round knockout of Gonzales in Tucson. All of that TV money from the networks goes to him, none to his opponent or the promoter. He's the talent. And there is no manager to cut in for the customary third, or 50 percent.

He could quit right now as a rich young man, owning U.S. treasury bills, money-market certificates, highrated state of Maryland tax freebonds, and a newly acquired five-unit apartment house in Silver Spring as a tax shelter.

He gets a computerized printout every month of all he owns, all that came in and all he spent, from his attorney's office.

One of his recent expenditures was for an engagement ring. He is going to marry Juanita Wilkerson, mother of their 2-year-old son, around Christmas time. They've already changed the boy's name from Ray Charles Wilkerson to Ray Charles Leonard Jr. Did a nice thing for his parents, too, with that $65,000 house he bought them; no mortgage.

Sugar Ray wasn't even the most famous of the smaller U.S. boxers to win golds in the Olympics. Howard Davis was, and CBS grabbed him up when he turned pro, gave him a long TV contract and now wishes it had Leonard, whose ratings are double Davis'

Leonard's people say they are keeping their TV option open by giving nobody an exclusive on Leonard. All the networks are eager to stage Benitez-Leonard for the title and will have to meet the price. As for Benitez demanding a bigger cut, as champion, than Leonard gets as challenger, Trainer scoffs at that stuff. He says they ought to ask ABC about the comparative ratings last month when Benitez defended his title against Harold Weston and Leonard fought No. 6 rated Gonzales. Out of the Benitez fight, ABC got a rating of seven. Leonard gave them a more significant 13, and Sugar Ray's people are telling the networks to put that in their computers. CAPTION: Illustration, no caption, By William Coulter for The Washington Post