"Watch out, Cassius. The jackals are out there and they will get you in the end . . ." Jimmy Cannon to Cassius Clay (a.k.a Muhamand Ali).

"They will try to break you because you are a symbol of a force they are unable to destroy . . ." Bertrand Russell.

Muhammad Ali will climb into the ring against Larry Holmes Thursday in Las Vegas to try to capture the World Boxing Council heavyweight title for an unprecedented fourth time. I think Ali might not win, and this is the first time I have thought so since his first Sonny Liston fight. I am forced to seriously address the question: What if Ali loses?

A loss shouldn't end the boxing career of the 38-year-old former heavyweight champion. He should have an honorable retirement for his adoring public, filled with memories of his greatness. A loss would crack that image.

It is important to an entire generation that Ali refused induction into the U.S. Army because he was a bona fide Muslim minister. That the Supreme Court vindicted him later attested as much to his stature as to the justices' belief in their 8-0 vote in his favor. Even today, as Bob Woodward and Scott Armstong wrote in "The Brethren," "He (Ali) did not know how close he had come to going to jail." A final loss now, clearly past his prime, would disillusion many who look forward to more grand acts from an honorably retired champion.

Ali was the first overtly political professional athlete in decades. Think what you will about "separation of church and state." Most people viewed his conversion from Christianity to Islam as a political statement. In the United States, any conversion from Christianity is seen as a political act by most.

To the casual sports fan, a loss to Holmes may be viewed as the inevitable culmination of just another great athlete's career. But closer scrutiny compels one to think again.

The boxing world, with its assortment of colorful figures, would lose its biggest draw. As with Howard Cosell, you don't realize how dull a sports event can be until he's gone.

A loss to Holmes for the WBC heaveyweight title also would mean a lower platform from which to speak later in life. Earlier this year, a black magazine publisher was planning a cover story on Ali unitl his ill-advised trip to Africa for President Carter. The bad press in Africa changed the publisher's mind.

Yet, Ali, the man, remains undaunted. "I'm going to shock the world for the sixth time on Oct. 2," he told me. "They don't believe I could whip Liston in '64; (Joe) Frazier in '71, or (George) Foreman in '75. They also didn't belive I was serious about Islam or refusing induction into the United States Army. Larry Holmes will be shock No. 6."

Though the braggadocio is there, the fire, zip and audacity we came to look for are lacking. His speech is notably more slurred. His hands are permantly gnarled from more than 50 professional fights. His left jab, once timed in an eye-winking 4/100ths of a second, is now about 8/100ths of a second -- twice as slow.

In many respects, this Holmes fight is a wrapping-up encounter. Like a tie breaker in tennis or sudden-death overtime in the Super Bowl, a loss now is measurably worse than some loss years ago. "I was the Greatest" doesn't sound quite right.

Not that he isn't pulling out all the stops. Ali has been sparring with two 175-pound, lightening-quick light heavyweights in addition to two young, promising 220-pound heavyweights. "My weight is down to 222 pounds from 253 and at fight time I'll be around 223."

Any predictions, Muhammand? "Sure. The bell won't ring for round nine. Holmes tires. He can't for more than six or seven rounds and he's not a heavy puncher. And he's a sucker for a left jab."

Is Ali fighting because he needs the money?

"I'm 10 times a millionaire right now. I've made $58 million and will make $16 million more this year -- $8 million from fightin' Holmes and $8 million more for (Mike) Weaver. I'll be four times the heavyweight champion of the world and still a lot of people won't like seeing a black man make that much money."

In Ali's autobiography, "The Greatest," there is a chapter devoted to the George Foreman bout in Zaire in 1974. Archie Moore, a Foreman supporter and former lightweight champion, proffered that George might kill Ali if he didn't watch out.

Moore attended one of Ali's public sparring sessions before the fight. Ali stopped sparring when he spotted Moore, and asked, "Archie, am I too old at 33?" Archie didn't answer. Ali asked again, "Am I too old?" Archie smiled and walked away. Ali returned to his workout. His sparring partner at the time who heard this exchange was Larry Holmes.

I'm going to Las Vegas to watch this bout. I must go because I feel it might be Ali's last. But I, too, fervently hope that in the end, the jackals don't get him.