THE FISTS OF THE THREE-TIME world heavyweight champion, Muhammad Ali, the Greatest himself, were headed straight at my chin. These were the hands that had dissected and demoralized Sonny Liston, then dumped him like old laundry; that had beat upon Joe Frazier so badly he could not go another round; that had reduced George Foreman from a Goliath to a beanbag. These were the hands whose unrivaled speed and precision had left an everlasting impression on the face of boxing. In a moment they might do the same to mine.

But I was oddly overjoyed to see this deft combination streaking toward me. I was almost laughing.

So was he, which was, under the circumstances, more reasonable.

The look was so familiar - as was the old routine of biting his lip as though seething in anger, the mock outrage in his widened unblinking eyes, even the pantomimed, taunting words: ''I'm gonna whup you!'' His face, virtually unmarked except for hairline scars hidden in his eyebrows, is still youthful (though he admits to dying his hair) and pretty. Ali's body still has power and remarkable grace.

His shoulders rolled rhythmically and he feinted with his hips, gliding sideways as he snapped off a half-dozen jabs from bizarre angles, all focused on approximately my puss.

We were in the family room at his farm in Berrien Springs, Mich., an 88-acre tract once owned by Al Capone. Recklessly, I teased him: ''You're old, you're slow - you're getting fat!''

I was actually hoping he'd land one -just one: so I could point at the bruise, feel it, however long it took to heal, and tell everyone how I got it. But instead he whistled one by my ear, caught me around the neck and pulled me into a clinch and broke up laughing while I hugged him.

I WAS VISITING WITH ALI BECAUSE I had been asked by Lorimar-Telepictures to research and write a new television-movie version of his extraordinary life story. He is remembered always as he was: seemingly immortal and omnipotent, dazzling and vital.

But the latest reports and rumors had it that Ali was depressed and physically deteriorating. He was described by some to be now in a final tragic chapter of his legend-in-progress. Before my first meeting with Ali, everyone I told about the project wanted only to know, ''Is he all right?'' His legion of fans has identified with him, agonized with him and now is frightened for him.

When I visited him on his farm one afternoon early this year, my own worst fears were quickly aroused. I was greeted by the farm's caretaker, Floyd Bass, who, in knit cap and gray beard, looked like George Carlin playing the world's oldest hippie. ''Muhammad's asleep in the truck,'' he said, gesturing at the beige Winnebago he was hosing down in the driveway, ''He gets kind of tired in the afternoons, I guess, with the medicine.''

Then Ali lurched out of this mobile home to greet me. His words seemed indistinct at first, and his face expressionless. As we walked toward the house he seemed unsteady. Then something odd happened. Walking down the driveway he slipped on a patch of ice and almost fell. But he didn't fall. Instead, without taking his hands out of his jacket pockets, he did a kind of modified Ali Shuffle, a quick two-step, and after a small hop, kicked one foot off a flower bed's retaining wall until he was on dry paving. He turned around without breaking stride, to warn me, now more distinctly, ''Careful -ice.''

A few minutes later, we sat on a couch in his family room. By one wall was a long dining table covered with stacks of yellow paper full of notations and references for a religious pamphlet he is compiling. On a sideboard was a picture of his family - seven daughters and a son by two of his three previous wives, and two other relationships. On the wall near the table hung a small framed picture of Joe Louis in his boxing prime. On a desk behind the couch was a computer with its recent printouts. In one corner, a television buzzed fuzzily - the cable company hadn't gotten far down the road yet.

Seated on the couch, Ali began to demonstrate his magic tricks. He has been amusing people with them for years, making silk handkerchiefs disappear by stuffing them into fake thumbs, and tearing up paper that magically mends itself.

I'd seem him do them at the victory party after the Tyson-Holmes fight in Atlantic City in January. For half an hour that night he had entertained guests with the same tricks - but depressed them with the obvious stiffness in his movement and his nearly inaudible voice, his expressionless face hidden behind dark glasses.

At the fight an hour before, the crowd had demanded him as the introductions of celebrities dragged on endlessly. They had chanted ''Ali! Ali! Ali! Ali!'' (He got a similar response from the crowd at the Tyson-Spinks bout last month.) And when he stood, they roared louder than they did even for Joe DiMaggio -let alone Larry Holmes and Mike Tyson - rising to salute him. But when he climbed into the ring he stumbled, and seemed to shuffle aimlessly across it. The crowd gasped and sat down raggedly, in shock.