Sugar Ray Leonard signed yesterday in Montreal in defend his World Boxing Council welterweight championship against Roberto Duran of Panama on Friday night, June 20, at Olympic Stadium. Leonard will receive between $5 million and $8.5 million for the fight.

Ringside seats will sell for $500, and the stadium where Leonard won a gold metal in the 1976 Olympics can accommodate 75,000. Duran, the former WBC lightweight champion who is now the No. 1 welterweight contender, will receive between $1.5 million and $2 million.

The bout will be shown on closed-circuit television in the Washington area at Capital Centre. Tickets bought in advance will cost $25 and on the night of the fight $30.

The undefeated Leonard, 23, said at the signing ceremony: "I'm happy to return to this city and be part of one of the biggest fights in history. I'm certainly not going to take Duran lightly because, pound for pound, he's the best fighter available for me to box.

"I'm in superb condition and I'm sure Duran will be in great shape. It's going to be a dynamite fight."

Duran, 28, said through an interpreter: "I don't talk too much. My business is fighting. But I think this is the first time Leonard will really have to fight."

Leonard and his attorney, Mike Trainer of Silver Spring, Duran and boxing promoters Don King and Bob Arum face a suit to prevent the bout from being held in Montreal.

Caesars Palace of Las Vegas asked Thursday in U.S. District Court in Baltimore for a temporary restraining order, contending that it has the right of first refusal on the bout because of an agreement it says was made in December.

The resort hotel said that, in anticipation of securing the bout, it arranged for construction of a temporary stadium to seat 24,000, and that 1,000 of 1,700 rooms had been reserved for celebrity patrons expected for the fight.

The suit alleges that King and Arum made agreements they knew they would not honor.

The suit further claims that, the day after King announced that Leonard and Duran would fight June 20, King offered Caesars Palace a package deal in which the promoters would get $3.5 million of the "live" gate receipts and the hotel would be reimbursed for advertising expenses from any gate receipts in excess of $3.5 million.

The hotel said it also was awarded closed-circuit television rights in Las Vegas and Lake Tahoe as part of the agreement.

In a telegram yesterday to Arnold M. Weiner, the Caesars Palace lawyer, Leonard's attorney reportedly stated, "Don King Productions Inc. at no time had the site rights to the Leonard-Duran title fight and was not authorized to negotiate" with the hotel on Leonard's behalf.