In January and February, Bob Arum, the promoter, devised for Marvin Hagler and Tommy Hearns a 21-city stop-and-go tour aimed at arousing public interest in their 12-round affair coming up here Monday. This was necessary because Arum is guaranteeing the two gladiators a combined payday of $11 million, and he would be much out-of-pocket if too many citizens were to remain indifferent to his expensive project.

At every stop, Hagler and Hearns obediently summoned their most wicked glares for the cameras and spouted their hate for each other. From coast to coast, the act was the same, with Hearns vowing dire consequences for Hagler and Hagler hurling his scorn at Hearns. They acted terrible.

It was pure cornball hokum, and everybody would recognize that. But it worked. The fight has seized the country.

Trying to buy any of the 15,128 tickets in Caesars Palace's stadium is useless. At prices starting at $600 per seat, reserved for the casino's top gambling clients, and ranging down to the $100 seats for the peasants, they were sold out six weeks ago. But that $6 million live gate is not where the big money is coming from. The important cash is coming from out there in closed-circuit TV land, where there is also a lively scramble for tickets. Seven hundred outlets, a record (the first Ali-Frazier fight commanded only 400), will show Monday night's battle.

In New York, a new, trendy prize-fight chic seems to be present. At the Tavern on the Green restaurant in Central Park, the closed-circuit is a sellout at $100 per person, including wine and dinner. At the fancy 21 restaurant, the owner will march 600 of his dinner customers to Radio City Music Hall across the street, where they will be his guests at the fight for $50 a ticket.

The returns from theater TV, Arum estimates, will hit $40 million plus, 45 percent of which goes to the exhibitors. Arum's own firm, Top Rank, sold the live gate to Caesars Palace for $4 million. Hagler and Hearns each could walk away with near $9 million paydays, with their percentages of the TV take after it hits $14 million.

"Put it this way," said Teddy Brenner, Arum's matchmaker. "Joe Louis, Jack Dempsey, Rocky Marciano, Sugar Ray Robinson, Tony Zale and Rocky Graziano, as a group, never made as much in their whole careers as each of these fighters will be paid Monday night."

Even the stiff-backed Internal Revenue Service got into the act as an unlikely shill. That master of puffery, Irving Rudd, an Arum aide, took to the IRS the idea that Hagler and Hearns could do a public service for that sometimes disliked government bureau.

The IRS bought Rudd's plan, and for weeks many of the nation's TV stations saw Hagler and Hearns on screen for IRS, posing in ring togs and saying things like, "Get your income tax returns in on time" . . . "Don't forget the deductions" . . . "And also the refunds" . . . "File early and then relax." From the unbending IRS, prizefighting was getting a new dignity and credibility.

When Hagler and Hearns were hurling their anathemas at each other on their long tour to promote the fight, it was actually not all hokum. They had genuinely learned to dislike each other.

"You can't have two men, especially upcoming rivals, traveling in such close proximity for so long without some hate cropping up," said Arum. "Hagler got tired of listening to Hearns' predictions he'd knock him out, and he also resented Hearns' stealing his lines at the press conference."

On tour, childishness also cropped up. Hagler wouldn't make an entrance at the press gatherings until Hearns showed up first. Hearns got sore at this, and threatened to quit, saying, "I can wait, too."

Worst of all, they blew this week's Sports Illustrated cover, according to Arum. "Sports Illustrated had everything ready and it would have been a big one for us, being on the cover. But Hagler refused to pose with Hearns, saying 'I don't want to be in the same room with him.' "

They also toured in two different jets. For Hagler, Caesars Palace provided its luxurious Gulfstream with its costly appointments, television, video games and a kitchen. For Hearns, Arum hired a less fancy jet. On the return trip from the West Coast, they would switch planes, the fighters had agreed. But Hagler reneged, threatening to go home to Brockton, Mass., if they took away his many-splendored plane.

So, Arum had to search for another fancy Gulfstream jet for Hearns, or have a mess on his hands. "I was lucky to find one for rent in Los Angeles, and Hearns was appeased."

Even Jake LaMotta, the old middleweight champ, was brought in by Arum to travel the scene and pump up interest in the fight. Jake was a big hit everywhere he went, Arum said. "And this week LaMotta is marrying his sixth wife. Jake tells people about an earlier wife who 'always complained she didn't have anything to wear; I never believed her until I saw her pictures in Playboy.' "

For its share of the live gate, Caesars Palace will reap a $2 million profit, but it is counting on many more millions contributed by those who will come to gamble during fight week. Like a good neighbor, Caesars isn't hogging the whole show. Of the 5,000 seats in the stadium's VIP section that Caesars Palace reserved, it is distributing 500 to each of six other hotel-casinos here. Its high rollers will be seen spotted among the celebrity crowd (Kirk Douglas, et al).

These are the $600 tickets, and according to the Las Vegas Review-Journal, the casino's president, Don Allison himself, is handling the seating arrangements with VIP chart in hand. It's the Las Vegas caste system at work.