IF, indeed, tonights heavyweight championship fight between the "Sphinx" and Leon Spinks turns out to be a "scam," it will be a victimless crime.

Although Muhammed Ali has not tried to erode the confidence of this challenger by denigrating him, the public must know by now that the bout is regarded as so one-sided that not even in this gambling capital have odds been established.

The champion will enter the ring with the largest weight advantage, 27 pounds, of his career. He weighed in yesterday at 224 1/4 pounds to Spinks' 197 1/4.

The four bout boxing program to be shown in the Washington area over WTOP-TV-9, will start at 8 p.m. The Ali fight isn't expected to start until at least 10 o'clock.

It will take place in the 5,500-seat Hilton Hotel sports pavilion and ring-siders will pay up to $200 a seat. The CBS Television Network is helping bankroll the prime-time show by charging up to $86,000 for 30 seconds of commercial time.

Ali will receive $7.3 million, plus $200,000 for expenses for exposing his 35-year-old body to whatever threat the 24-year-old former Olympic light-heavyweight champion can muster.

Spinks will receive $300,000 plus $20,000 for expenses, plus what soon may become a rare entry in a boxer's record: the saleable distinction of having fought The Great One.

The public's best protection against a grand seam is Ali's history as the real trouper, the showman who always manages to keep his opponents around long enough to satisfy the relatively normal expectations of the live promotion and the network.

Of course, there is an inherent risk in these times, when it is said that Ali's energy resources are so limited that he cannot put together two busy rounds. The gamble is that if he is able to knock out Spinks in an early round and delays doing so, he might run out of gas before he can apply the coup de grace.

As a change of pace he adopted a pretty-much-kept vow of silence. The suspicion is that he slickly evaded persistent questions of how he could justify a defense against a youngster with only seven professional bouts.

Likewise, he did not have to answer for putting of f a defense against the obvious No. 1 contender, Ken Norton.

Jose Sulaiman, president of the World Boxing Council, admitted here yesterday that if Ali and Norton sign by July 7, the fight can be put off until autumn.

There wouldn't have been more decorum at the weighting-in ceremony had Silent Gene Hairston beem on the scale. In contrast to previous demonstrations at these affairs, such as the tantrum he threw before his first bout with Sonny Liston, Ali went onto the scales quietly. Finally he was asked "Is there anything you want to say?"

Spinks either appreciated the champion's sparing him vocal abuse or the fact that Ali has given him his big chance in the ring tonight, because the challenger was seen applauding politely as Ali was introduced. Ali did try to make eyeball contact with Spinks a few times, as if tempted to fix one of his trademark stares on him, but was not successful.

Spinks seemed happy just to be here when he asked to comment about his weight. "I'm satisfied with everything " he said.

Ali's previous lightest championship opponent was Henry Cooper of London, who weighed 188. But Ali weighed 201 1/2 then. Floyd Patterson weighed 196 3/4 for one of his two title bouts with Ali, and Ali weighed 210.

Spinks has not indicated that he is capable of knocking out a champion who has been extremely able to take a punch. Nor does the challenger hace Ali's cleverness.

Spinks keeps coming on, willing to take punches to keep up a steady pressure. But, again, he is not yet nearly as effective at that as, say, Joe Frazier was. Spinks does not jab well and seems uncertain how to get under one. Although his hands are fast, his feet do not carry him with anything like the grace of Ali.

The champion has not boxed, at least publicly, since Feb. 6. In training he settled for daily roadwork and hitting the heavy bag, although he seemed to spare his right hand, which usually requires a pain-killing injection because of arthritis and calcium deposits.

Ali apparently decided he did not need to learn how to box after 57 bouts and that he had been better served by saving the energy.

Ali had difficulty with contenders such as Jimmy Young. Ernie Shavers and Norton since winning a life-and-death struggle against Frazier in Manila in October 1975. Even Alfredo Evangelista was able to go 15 rounds with him.

In fact, Ali has had four 15-round bouts since knocking out Frazier in the 14th. Spinks will be trying to go 15 for the first time. He had 185 amateur fight and won 178. 133 by knockouts. But those bouts, of course, were scheduled for three rounds.

He won his first five pro fights by knockouts. But when he encountered journeyman Scott LeDoux, he could only pull out a questionable draw over 10 rounds and he had to go 10 rounds to defeat another run-of-the-mill boxer. Alfio Righetti.

Spinks says it is his youth against Ali's experience. He also notes that he nas never been knocked down or out.

Taking on all comers, some like Frazier and Norton as many as three times. Ali has won 55 of his 57 bouts, 37 by knockouts. He has never been stopped. He lost his first fight with Frazier by decision and his first with Norton by decision, but in that contest his jaw was broken in an early round.

In other bouts, Micheal Spinks, the challenger's younger brother and the Olympic middleweight champion, meets Tom (The Bomb) Bethea of New York; Danny (Little Red) Lopez of Alhambra, Calif., defends his WBC featherweight title in a 15-rounder against former champion David Kotei of Ghana, and light heavyweight Jesse Burnett of Los Angeles takes on Eddie Gregory of New York.