Mr. Brokaw said Mr. Cosby, who was in Philadelphia yesterday taping his new syndicated television series "You Bet Your Life," would have no comment on the offer..

But Mr. Brokaw denied some news reports yesterday indicating that the deal was dead. "This is a real story," he said. "Bill authorized me to come to New York and meet with Bob Wright."

And Mr. Chaice said: "We understand they said NBC is not for sale. What inferences you can draw from that I'm not sure of. But in my mind, everything is for sale. It just depends on what the seller and buyer agree upon."

As it has done in the past, NBC declined to comment on the possibility that the network might be sold.

But one senior NBC executive, who spoke on condition of anonymity, said that Mr. Brokaw had exaggerated the seriousness of his discussions with Mr. Wright.

Mr. Cosby's personal wealth has been estimated at $300 million. The entertainer owns a substantial piece of "The Cosby Show," his longtime comedy hit, which was produced by the Carsey-Werner Company and ended an eight-year run on NBC last spring. Mr. Brokaw pointed out that syndication sales of reruns of "The Cosby Show" to local television stations were very strong. "The show is approaching $1 billion in syndication," he said. 'Warm Feelings' About NBC

Mr. Brokaw characterized Mr. Cosby's interest in buying the network in personal terms. "Bill has very warm feelings about NBC," he said. "He got his break there almost 30 years ago in 'I Spy.' Then he had the most financially successful show of all time there in the 1980's."