When Marvelous Marvin Hagler -- he went to court to become "Marvelous" legally -- meets Thomas "Hitman" Hearns in the ring at Caesars Palace in Las Vegas tomorrow night, the event is going to make boxing history.

The two fighters stand to gross more money for themselves and their promoters than has ever been made in a single bout: possibly $50 million in all. And the closed-circuit telecast of the 12-round middleweight championship will be seen by more people -- an estimated 2 million -- than ever before.

Everyone with even a passing acquaintance with boxing is talking about "The Fight."

One of the 700-odd locations in the U.S. and Canada where there will be closed-circuit TV is New York's cavernous Radio City Music Hall. The first buy of tickets there, said Robert Arum, chairman of Top Rank Inc., the fight's principal promoter, went to Sheldon J. Tannen, who runs New York's tony 21 Club restaurant. Tannen bought 600 at $50 apiece.

"What he does is make a big dinner before the fight," said Arum, who was once a tax lawyer in the Justice Department. "Then, everyone walks over to watch the fight, and afterward they all come back to 21 and get bombed."

This is by no means an East Coast phenomenon, notes Arum. "Jerry Perenchio, Norman Lear's partner, called me up and said, 'Look, I've got a bad back, and I can't come to Las Vegas, and I want to have a dinner party for 60 of my friends in a private room at Chasen's a fashionable Los Angeles restaurant frequented by movie moguls . So we're charging him $5,000, and he's having some friends over for dinner to see the fight. This is happening all over the country."

Adds the Brooklyn-born Arum: "It is not a dees and dems kind of audience."

Perhaps not. But recently, Top Rank's press agent, Irving Rudd, came barreling out of his office, saying he'd had a call from a long-lost friend and "he wants to know if we can make some sort of arrangement so he and his friends can watch the fight."

"If he's got money, what's the problem?" Arum asked.

"Well," admitted Rudd, "he's in prison."

The Hagler-Hearns fight is commanding such attention and money because two such exceptional fighters seldom exist at the same time in the same weight class. Hagler, 30, from Brockton, Mass., has a record of 60 victories, 2 losses and 2 draws, with 50 knockouts. Hearns, 26, from Detroit, has 40 victories, 1 loss and 34 knockouts.

Professional boxing is splintered into three groups: the World Boxing Association, the World Boxing Council and the International Boxing Federation. Thus, there can be as many as three champions at once in any class. Hagler is the undisputed middleweight champion in all three groups. Hearns is the WBC super welterweight titleholder.

The weight limits are 160 pounds for middleweights and 154 pounds for super welterweights. Tomorrow, both Hagler and Hearns will weigh in at about 159 pounds. If Hagler loses, Hearns is the undisputed middleweight champion. But if Hearns loses, all he loses is the fight; he retains his welterweight title.

For 36 minutes of work -- albeit at the end of two months of training -- the two fighters will split a guaranteed minimum of $11 million, with Hagler taking a fraction more than half. But if the closed-circuit audience is anywhere near as big as Arum expects, Hagler, Hearns -- and Arum, too -- each will take home considerably more. Once Arum covers the purse and his $3 million in expenses, Hagler gets 45 percent, Hearns 35 percent and Top Rank 20 percent.

Here is where the money comes from:

Caesars Palace, which has about 15,000 seats, has tickets selling for as much as $600 at ringside, with the average ticket selling for $400. Seats were sold out about a month before the fight. Of the $6 million total, Top Rank gets $4 million.

On the television circuit, tickets range all the way from $100 at New York's Tavern on the Green, where dinner and wine is included, to $15 at some race tracks. Arum estimates that the average will be somewhere between $20 and $23, or $40 million to $46 million, of which the exhibitors keep 45 percent. Top Rank gets the rest.

In some areas, mostly in Southern California, there will be pay home television, targeted to bring in another $6 million, with $3 million of that going to Top Rank.

Finally, Arum will get as much as $2 million more from the sale of everything from T-shirts to advertising signs on the ring posts. This will put Top Rank's gross revenue between $24 million and $30 million, said Arum, whose press-kit biography describes him as "an outstanding Talmudic scholar."

Fight promotion was the last thing Arum intended to do when he graduated from Harvard University law school in 1956 and entered business as a tax specialist. In the 1960s, he left private practice to head the tax division of the U.S. attorney's office for the Southern District of New York. It was in this capacity that he was put in charge of a case involving a fight between heavyweights Floyd Patterson and Sonny Liston. The Internal Revenue Service feared that the fight's promoter, Roy M. Cohn, would take the proceeds to Switzerland in a complex arrangement to defer payments to the fighters, a procedure that was contrary to IRS rules at the time. So Attorney General Robert F. Kennedy ordered Arum to seize the money, including income from closed-circuit television.

"I didn't know anything about the business or about boxing," said Arum, now 53. "But I took depositions from Liston and Patterson and Cohn, and I became fascinated. I took depositions for weeks, and by the time they were over, I knew everything there was to know about the boxing business."

In 1964, Arum joined Louis Nizer's law firm, where he specialized in boxing and TV negotiations. That's how he met Jim Brown, the former Cleveland Brown football great who had become a boxing commentator.

"Jimmy said, 'Hey, you shouldn't be just a lawyer -- you should be a promoter,' " Arum recalls. "I told him I didn't want to get involved, that the only person who made any money from fighting was Muhammad Ali. But Jimmy said he knew Ali, and he set up a meeting and we hit it off from the beginning." Arum, Brown and others started a company, Main Bout, to promote Ali's fights, and Arum was hooked. He has been a fight promoter ever since.

He promotes between 20 and 30 major fights a year, along with a weekly contest for beginning fighters on the ESPN cable network. His office is filled with pictures of pugilists, and along one wall there is a stack of Mexican boxing gloves. "Because of currency restrictions, I can't get pesos out of Mexico," he said. "So they pay me in gloves and adhesive tape."

There will be no such nonsense with the Hagler-Hearns fight. Closed-circuit tickets are selling briskly in the U.S. and Canada. And it may be that the flood of buying has just started. There is a strong correlation between the amount bet on boxing and the number of fans who decide to watch a fight to see if their man wins.

"We are getting reports from Nevada that there is already the highest action for any fight in history," Arum declares. "They already have some bets as high as half a million dollars. I would expect legal and illegal bets combined will reach $1 billion."