Mike Weaver, the World Boxing Association heavyweight champion, will fight top contender Gerry Cooney at Ceasars Palace Oct. 22, boxing sources reported tonight.

The WBA on Wednesday ordered Weaver to make his next defense by Sept. 30 against James (Quick) Tillis, the No. 2 contender, or face the loss of his crown.

An official announcement of the date and site of the Weaver-Cooney fight is expected to be made in a few weeks, the sources said, adding that the contracts were signed last Sunday.

The WBA, after a meeting in Houston, had ruled that purse bids by promoters interested in staging the Weaver-Tillis fight would be accepted until July 15. Weaver then would have another 10 days to sign with the promoter making the best offer.

But Don Manuel, Weaver's manager, said Thursday there was no chance the champion would agree to meet Tillis before fighting Cooney; that Weaver was signed to fight Cooney for a $3 million purse in October in Las Vegas.

If the WBA stripped Weaver of his title, Tillis and Greg Page, the No. 3 contender, probably would meet for the vacant crown.

Cooney's comanager, Dennis Rappaport, would not confirm or deny the signing.

"There's nothing definite for that day," said Rappaport, who was reached by telephone at this home in New York. "It's still open, there's nothing definite. But that is one of the days that has been mentioned."

According to a source, the fight will be held in a 24,000-seat arena, the same arena that the Sugar Ray Leonard-Thomas Hearns welterweight title fight will be staged Oct. 16.