Bob Arum is so certain that Leon Spinks will fight Muhammad Ali Sept. 15 in New Orleans that he can hardly wait for an official announcement next Thursday.

"It's going to be one heck of a news conference, with all the nostalgia in the city where James J. Corbett knocked out John L. Sullivan for the title in 1892," Arum said yesterday in New York City. "Joe Frazier defended his title there against Terry Daniels in 1972. This one belongs on home TV and I expect to conclude a deal with a network."

How can a network afford what Arum says will be a promotion costing upwards of $10 million?

"Well, the people in New Orleans are paying $3 million for the rights to the 'live' gate. Foreign television and radio rights should bring about $2 million.

Reminded that would leave a cost of $5 million to $6 million for a U.S. network, Arum pointed out that CBS paid $4.1 million for the first Ali-It will be historic."

Arum said the promotional group in New Orleans, paid his Top Rank firm Wednesday a "good-faith, substantial deposit" of $300,000.

"We signed an agreement in principle - I call it a contract," Arum said. "Now they have to finalize some local merchandising arrangements about concessions and suvenirs and so forth in the Superdome (71,330) capacity for football).

"I have to get the approval of the fighters, but they already have agreed orally. I'm going to Chicago Friday to sign Ali and to Detroit Saturday to sign Spinks the boxers will receive $5 million each).

"CBS has an option on the bout that will include paying both fighters' training expenses and $200,000 each for three other championship bouts which will be on the show. The principals in those bouts will be determined in fights being developed."

In reponse to a question, Arum said the Superdome was selected over Madiso Square Garden "because the Garden was not as agressive. The New Orleans people are crazy about the bout."

He said that a proposal from an African group was rejected because, after tentatively agreeing to conduct the bout in Swaziland, the group then requested to put it on in Bophuthatswana.