The promoters of the $30 million fight here were heard to develop a rattling sound in their throats today during a two-hour medical examination of Roberto Duran and the disclosure of a "mystery" virus that cast doubt on the condition of Sugar Ray Leonard for Friday night's championship bout at the Olympic Stadium.

At a news conference following Duran's workout, promoter Bob Arum said he was satisfied with the results of the exam this morning on the challenger from Panama. Arum said the fight would go on.

Dr. Guillermo Gonzales, a heart specialist from Panama, was asked to fly here by Duran's manager, Carlos Eleta, and he participated in the examination at the Institut de Cardiologie de Montreal.

Gonzales said through Luis Henriquez, interpreter-trainer for Duran, that the fighter's "health condition is perfect."

It was disclosed that Duran underwent a heart examination at Notre Dame hospital here last Thursday and the cardiograph showed "a couple squiggly lines where they shouldn't have been," according to Arum. Gonzales said the first test indicated "an abnormality that indicated further testing was advisable to be certain."

Arum said that he; Jose Sulaiman, president of the World Boxing Council; the Montreal Athletic Commission; Eleta, and Gonzales thought it "best for all concerned to publicize the tests."

Gonzales said there has never been the hint of a heart problem with Duran. The physician said the tests had no relation to an examination for a back injury that Duran underwent in New York City two weeks ago. Gonzales said the examination Thursday was unusual. He said it was difficult to explain.

Sulaiman of the WBC said, "We have this happen maybe five to 10 times a year; that the test doesn't come out just right. It doesn't necessarily indicate a sickness, just a doubt."

In his eagerness to assure the media that Duran was fit to fight, Arum said in front of Gonzales: "Duran not only passed the test with an A-plus, he was in such perfect shape . . . so strong that he broke certain instruments."

The news conference was held at the Paul Sauve sports center, after Duran worked out with great enthusiasm.

Usually only relatively communicative because of embarrassment at his inability to speak English, Duran played to the spectators for the second straight day.

As if impatient about not being permitted to spar today, he punched at the padding in the corners of the ring, occasionally whirled in the manner of a dervish and waved at the crowd and exchanged remarks in Spanish to countrymen in the stands.

Duran again made references to Leonard in his remarks to the fans, and mimicked the champion by bending over with his buttocks extended and jabbing daintily and ridiculing Leonard's shuffle as the fans applauded.

Earlier, after a public workout in the lobby of the hotel that is the fight headquarters, Leonard dropped a minor bombshell at a news conference in the press room when he was asked about his weight.

"I weighed 149 pounds this morning (two pounds over the welterweight limit)," he said. "I probably weigh 144 or 145 since my workout. I'd like to be 149-150. I've had a virus coming on for a week."

Was he running a fever?

"No, just a little sore throat once in a while. That's why I was down to 143-144 last week. I'll bring my weight up."

Leonard, who sounded raspy, boxed Monday for the first time in 10 days.

Was he worried about being overtrained?

"No, I feel great," he replied.

Trainer Dave Jacobs was asked if Leonard had consulted a physician or had had any treatment for the "virus."

"Doctor? No." Jacobs said, "Virus? That's the first I've heard of it.

If he had a virus, it wasn't that bad or I would have heard of it."

Jacobs said Leonard has boxed an aggregate of 207 pounds. But he went 15 rounds in one day only once, two weeks ago. "I don't think that's too much; I've been with Ray since the start of his career."

Leonard was isolated with sportscaster Johnny Holliday of Washington, who was taping his remarks. Leonard, with a wink to his two interviewers asking about his condition, said, "As a matter of fact . . . on the subject of a virus and a cold -- you guys being my friends. I don't have a cold, I was just talking." And he winked again.

The inference drawn before the interview was interrupted was that Leonard was trying to snatch the psychological advantage away from Duran, the underdog and challenger.

If, indeed, Leonard does have a health problem, it could be exacerbated because the bout will be outdoors and the nights have been chilly here, with the temperatures as low as the 50s.

Because of the possible impact of the news on the live gate, Arum was asked what the present advance sale is for Olympic Stadium. "I hear 30,000 tickets," he said.

Reminded that 41,000 was supposed to be the break-even figure for the Montreal government agency underwriting the bout, he said. "The scaling of the seats was stupid. All the $500, $50 and $20 seats will be gone (by Friday) but not the others (among 77,000)." He said the closed-circuit television seats were "selling out everywhere."

Las Vegas oddsmaker Bob Martin said from Miami when informed of Leonard's "virus." "The odds will drop some when people read that. People will back away. The trend for the last few days had been toward the underdog -- Duran. They tell me four of every five bets are being placed on Duran, but two large ones were on Leonard.

"The odds favored Leonard at 8 to 5 before this news."