"Don't let the system use you up," poet Nikki Giovanni said in admonishing those who venture beyond the bounds of reason. And in the case of former heavyweight champion Muhammad Ali, those bounds are not the ropes around the ring.

Ali, as everybody knows by now, is seeking to become the heavyweight to win the title four times. Most people think that he could do it, but many really don't want him to try, including me. I've asked dozens of people, sports fans and Ali lovers, what they thought of his comeback. Only a few thought he should try.

"Hell, $10 million ain't no drop in the bucket, even to David Rockefeller," one New York cab driver said. He added, "I'll get in the ring with Ali myself for that kind of money." When I inquired whether he believed Ali needed the money, he replied, "If all I got to show up and I get my $10 million, my needin' changes to wantin'."

After we both laughed, this taxi driver, who happened to be black, got serious for a minute. "The man (Ali) stared (Uncle) Sam in the face and told him 'I'll go to jail before I go to Vietnam.' Ali reminds me of Paul Robeson in the 50s; he wouldn't back down either.

The cab driver said he wouldn't miss any of Ali's upcoming fights.

While the cabbie spoke forcefully for Ali to fight again, amlost everybody else disagreed. "He's gonna get his brains scrambled." "He's over the hill." "The legs are gone, he can't shuffle anymore," were typical comments. Concern for his health was genuine and paramount. And interestingly enough, no one I asked wanted to see Ali fight and lose. There was no vindictiveness over his loud mouth.

Billie Jean King got the same advice after her last knee operation: "Quit while you're ahead." She answered that by recently defeating Martina Navratilova, the world's No. 1 woman tennis player, 6-2,6-0.

Examples abound of professional athletes who let the system "use them up." But with Ali, the boxing world is more interested now in not being embarrassed by an overweight ex-champion. Rodrigo Sanchez, president of the World Boxing Association, was taken aback at recent unflattering photos of a 250 pound Ali. Sanchez is demanding a tuneup to ascertain Ali's fitness.

While neither current champ, John Tate nor Larry Holmes, is afraid of Holmes.

All professional athletes come to that period of reckoning when we must look in the mirror and admit that it's time to stop. But the Gordie Howes of the world spoil it for us. At 51, Howe just scored his 800 goal in the National Hockey League. And Ken Rosewall still was winning Grand Prix tennis tournaments at 43. So we keep trying, and most of us never want to hear or say the word, "enough."

But boxing is different. It is a violent sport which the fighter's business is "to hurt people," as Sugar Ray Robinson once said. With all the recent furor over deaths in the ring, I'm sure the refrees of Ali's fights will make sure the ex-champ doesn't get hurt, no matter how much money is involved.

So Ali is sweating it out now at gymnasiums from Deer Lake, Pa., to Miami Beach to Los Angeles trying to bring his weight down to about 220 pounds by May 30. His fans will begin to sweat also. Too many fighters in the past hung around too long and wound up basket cases.

While I don't believe such a fate awaits Ali, I just hope he trains for his upcoming fights like there's no tomorrow. If he doesn't, that just might be the case.