This is a heavy scene, freak-wise. They're all here for all here for what Muhammad Ali has has promised (again) will be his last fight. Norman Mailer and Hunter Thompson have fresh haircuts and look sinfully healthy. LeRoy Nieman's mustache is approaching Dali status. Cheryl Tiegs is working for ABC-TV, kind of silent-beauty counterpoint to Howard Cosell.

Small wonder, then, that no one paid much attention to Matilda the kangaro.

Leon Spinks, the champion, was skipping rope to the frazzing beat of "One Nation Under a Groove," a disco song by the Funkadelics. This was in Municipal Auditorium. Maybe 500 people had paid $3 each to watch the workout, and here came this guy dressed in a kangaroo suit, hopping.

The kangaroo wore an Australian bush hat and boxing gloves.

The kangaroo hopped around a lot, shadow-boxing and all. But, sad for kangaroo-dom, no one cared. An Ali heavyweight championship fight is the big time, freak-wise, and the kangaroo was in over its head.

"The movie, 'Matilda,'" the kangaroo said (in a male voice) when asked to explain itself. In that movie, a kangaroo fights for the heavyweight championship. "I'm getting paid to do this trick," the kangaroo said, adjusting its bush hat.

Once true sports events in the fashion of a World Series or Super Bowl, Ali's fights long ago moved up a notch or two becoming social statements.

At the end of his exile in 1970, when Ali fought for the first time after three years of hassles with politicians, he was taken as a symbol of principle by liberal whites and he became a walking, talking, fighting reminder of independence to blacks.

Given such mythology and given Ali's insatiable appetite for adulation, it was inevitable there should grow up around him a circus. "The Ali circus," is what the 18 years of Ali have been called by Ferdie Pacherco, once Ali's fight doctor. The circus has played the world, from London to Manila, Kuala Lumpur to Kinshasa, Louisville to New Orleans.

And now, maybe, the merry-go-round is spinning its last.

Everyone seems determined to grab one more ride.

The lobby of the New Orleans Hilton is the bivouac for Ali's worshipers. The hang around the elevators, waiting to see The Greatest come down from his 17th-floor suite. Young men with songs they've written . . . artists with paintings . . . photographers, panhandlers, women in artery-closing jeans and high heels . . . they wait for Ali.

They carry their hearts on their sleeves. Or at least on their T-shirts. In the cottage industry that has grown with Ali's ascnesion from athlete to mythological figure, a T-shirt insisting "Still The Greatest" sells for $7.80. A quick survey shows that a complete wardrobe of nine Ali T-shirts would cost $75.80.

Nor by T-shirts alone can one express admiration for Ali, who, after all, shares in the proceeds. While staring at your Ali poster ($9), you might munch an Ali candy bar (45 cents) in eager anticipation of tonight's postfight party that promises music by Issac Hayes and an appearance by Ali (at $75 a ticket).

During Super Bowl week in New Orleans last January only revelers of great desire could push their way to the bar at the Absinthe House, a night spot on Bourbon Street. Oillionares from Texas and cowboys from Colorado were eight-deep at the trough. Hundreds more waited in lines outside.

Intrepid sociological reporters let no hardship stop their research, however. So we moved on the Absinthe House three night ago, there to test the night life for the Spinks-Ali fight.

Of 13 men in the place, 11 were sportswriters.

"Where's the fight crowd?" a native shouted to the barkeep. "Looks like they were to the A&P, got a loaf of bread and a pint and boarded themselves up in their rooms."

The Club 500 is a grungy-dungeon strip joint on Bourbon Street. The master of ceremonies, Joey Howard, introduced a callipygian terpsichorean by saying. "This next one is tall, gents. Talllll. She'd make a good sparring partner for Ali. Let's hear if fo Susan Little."

During a slow part of Too Tall Susan's performance, someone in the place called to her, "Who you like in the fight?"

From the face Susan made, you'd have thought she had never been asked such a question in the middle of undressing. At length, she said, "Ali. Uh-huh, Ali."

Leon Spinks is an afterthought here. His astonishing upset of Ali last February made him the champion, but here he is more dead weight on the merry-go-round than champion. For years, Ali has warnehd us that when he is gone, boxers again will be mumblers saying nothing. Leon Spinks is fulfillment of that prophecy.

As the merry-go-round spins down, heavy with time, a certain frantic effort is being made to keep it spinning, in memory if not in reality. T-shirts need be sold, TV commercials are at stake, movies can be made, millions of dollars are Ali's for the next fight. One more, Ali.

"No, no.I hope this is the end," said Gene Kilroy, for 10 years Ali's righthand man in a 20-man entourage. "Anybody who loves Ali doesn't want to see him hit on. Anybody who says, 'Champ, we gotta fight again,' is just looking for another payday."