Sugar Ray Leonard defends his World Boxing Council welterweight championship Friday night against Robert Duran in the richest prize fight in history.

Leonard, who grew up in the Washington suburb of Palmer Park, Md., and still lives in the area, will receive $8 million for the fight, with other potential income bringing him an additional $2 million.

Duran, considered one of the greatest fighters ever in a non-heavyweight class, will be paid $1.5 million, tax free.

Muhammad Ali earned $6 million for his "Thrilla in Manila" fight against Joe Frazier in 1975. Not since that classic struggle, won by Ali in 14 rounds, has a boxing match generated as much money for the fighters of interest.

The 24-year-old Leonard, who has won all 27 of his professional fights, plus an Olympic gold medal here four years ago, is a 3-to-2 favorite.

Oddsmaker Bob Martin, here for the fight, said the betting line changed from 9-5 on Monday to 8-5 on Wednesday to 3-2 today. "The trend has been all toward Duran the last couple days," Martin said.

Duran has won 69 fights and lost only once, to Esteban DeJesus in a 10-round nontitle fight in 1972. Duran, king of the lightweight division for nearly 10 years before becoming a welterweight, later knocked out DeJesus twice.

The fight is scheduled to begin between 10:30 and 10:35 p.m.

A relatively exclusive audience of about two million will pay as high as $30 each at 310 locations to see the closed-circuit telecast, from among the tens of millions accustomed to seeing the Super Bowl, the World Series, and Ali's last several bouts on home television. Tickets for the telecast remain at the D.C. Armory, but not at Captial Centre. The close-circuit telecast could generate $22 million, nearly double the take of any of Ali's fights.

An irony is that the "live" promotion in the Olympic Stadium may fail to achieve a break-even attendance of about 55,000. The stadium seats 77,269. t

There will be no radio broadcast, and no full-length tape of the bout will be shown until July 19.

"La boxe imaginaire," or shadow-boxing, is over, as the French-speaking announcer said at the last workout on Wednesday; a king's ransom in gold is on the table.

The official weight-in will be at noon Friday in the stadium. Leonard hit the exact 147-pound limit in an "unofficial" ceremony on Wednesday. Duran was 153.9 wearing jeans and desert boots, but said he was 148 stripped at the sports center where he trained the same day.

The ring officials formally will be named on Friday. There was an unofficial report that Carlos Padilla of Las Vegas will be the referee, who will not have a vote in the judging, that the voting judges will be Harry Gibbs of England, Anglo Poletti of Italy and Raymond Balderous of France.

Upon hearing that report, Duran's management objected to Padilla, contending his record of officiating would be to the challenger's disadvantage because in the past he has not permitted substained infighting. Angelo Dundee, Leonard's chief second, said he would be satisfied with Padilla, Leonard being most effective at long range.

Though both boxers were reported as being in "perfect condition" after examinations by the Montreal Athletic Commission physician before the "unofficial" weigh-in on Wednesday, they will be tested again during Friday's weigh-in.

Leonard has gone unbeaten since winning his gold medal here in 1976, but has not yet won complete acceptance from observers, who have been saying, "He'll become a professional against Duran."

The champion has scored 18 knockouts in 27 victories, but Duran says Leonard has been fighting "dead people."

Leonard has been saying of Duran's age, 29, "I don't want critics saying 'Duran was old' when I fought him."

The Panamanian turned pro at 15, won 27 straight bouts, 22 by knockouts. He knocked out Ken Buchanan of Scotland in the 13th round for the lightweight title in 1972.

Fifty-five of Duran's victories have been by knockouts, for a .775 percentage. Eighteen knockouts came in the first round, matching Leonard's knockout total. Duran has scored more first-round knockouts than Leonard, World Boxing Association champion Jose (Pipino) Cuevas, Wilfred Benitez and Tommy Hearns combined. He has scored 27 knockouts within three rounds.

Since moving up to the 147-pound class he has scored four knockouts in seven bouts.

His most impressive showing was in a 10-round decision over former WBC welterweight champion Carlos Palomino.

Both Duran and Leonard decisioned Adolfo Viruet.

Leonard took his hardest punch from Marcos Geraldo in winning a 10-round decision. The champion said he had "double vision" for a round and a half from that punch. Otherwide, he has not taken sustained punishment and that is the big question to be determined by Duran -- whether Leonard can stand up to two or three straight rounds of heavy body blows.

On the other hand, Duran had slowed noticeably in the last five years and since he moved up to 147 pounds.

Leonard has lightning hand and foot speed and fast moves, but he also punches with power and is deadly at finishing off an opponent in trouble. He has scored 18 knockouts, the last accomplished with a picture-perfect left hook that flattened David (Boy) Green in the fourth round March 31 at Capital Centre.

The victory was the first defense of the title he won by stopping Benitez with six seconds left in their 15-round fight Nov. 30.

"I want to beat Duran at his own game," says Leonard.

"I have no respect for Leonard," says Duran, whose game is intimidation.

Leonard is faster than Duran and snaps off his punches better. Where Duran's punches wear down opponents, Leonard floors them with one punch. He does not figure to be a stationary target for the challenger's body-punching.

Leonard's best hope would be to cut up the Panamanian with his cobra jabs and left hooks and then finish him off. Leonard has gone 15 rounds only once -- or six seconds short of that distance -- against Benitez.

Duran had gone 14 rounds twice and 15 rounds twice.

The experts suggest that one of Leonard's weaknesses is that he drops his left hand after delivering a jab or hook, leaving himself open to a right cross.

On the other hand, Duran often leds with a right hand. It is said to be the classic risk -- one that might be beaten by Leonard's faster left hook. b

In appraising Duran's effectiveness in his move up to the welterweight class, an analogy is made to a move up from the welter- to middleweight class by Sugar Ray Robinson.

"Robinson was an excellent middleweight," the experts say, "but he was a great welterweight."

The Montreal government agency that paid $4.15 million for the rights to the "live" gate originally said it would need to sell 41,000 sets to break even, but on Wednesday raised that figure to 55,000 because of unanticipated extra expenses. A sellout at the 72,269-seat stadium would represent a $7.6 million gate. By early today 34,000 seats had been sold, according to copromoter Bob Arum.