In the next day or two, Laffit Pincay Jr. will reach a milestone never approached by any other jockey. His mounts in a single year will have earned more than $8 million.

Because of inflation this record will not last long, and it might not even mean much. But Pincay's achievements transcend statistics. And for the people who have watched him ride this fall, the memories of his extraordinary feats will outlive any official records.

Jockeys usually win races because they happen to be riding the best horses. Their most important contributions are of a negative variety: good riders avoid committing serious mistakes.

But during some rare periods, a jockey will perform with such consistent brilliance that he becomes a dominant force. He seems to be able to transform the horses he rides. He seems touched with magic. Steve Cauthen rode this way during the one remarkable year when he became a national hero. Now Pincay is doing it, too.

Cauthen took the racing world by storm because he was a fresh-faced newcomer. Pincay has already done so much that it seems inconceivable he could still startle anyone with his talent.

At the age of 32, he is already enshrined in the Racing Hall of Fame. He is the second-leading money-winning rider of all time. He is one of nine jockeys in history who have won more than 4,000 races.

And yet Pincay recognizes that 1979 is not just a continuation of a great career. It has been, for him, a whole new beginning. Others may perceive him as a better rider this year; Pincay perceives himself as a different person.

Since he began riding as a 17-year-old in Panama, Pincay has been simultaneously blessed and cursed. His blessing is the enormous aptitude than made him an immediate success in his native country and two years later, in the United States. His curse is a chronic problem with his weight.

"The first horse I rode," he remembered, "I had to lose six pounds to get down to 100 and make the weight." When he was in his 20s, he had trouble staying light enough to ride at all.

This was the dominant fact of his life. "I'd get up in the morning, work horses, then put on jogging clothes and run a couple miles around the track, then spend 40 minutes in the sweatbox. After all that I'd go out there and ride seven or eight or nine races a day. And I'd be doing it all on an empty stomach."

Even with this regimen, Pincay often found himself losing the battle, so he resorted to diet pills to help him. Eventually he became dependent on them.

Anyone who has ever ingested one diet pill knows that they do not exactly foster a feeling of tranquility. The cummulative effect of them predictably affected Pincay's personality, making him tense and obsessive.

"I was so intense about winning all the time that I didn't want to accept defeat," he said. "If I made a mistake I'd think all day about what I did wrong. I got a lot of suspensions; there was a period when I'd rather win and get disqualified than lose. There were a lot of times when I would think about quitting racing and ask myself: "Is what I'd be doing worth it.'"

Feeling guilty about his dependence on pills and worried about their effect on his health, Pincay quit them and adopted a new diet. To anyone else, it might seem like torture. Pincay eats grains, cereals and fruits, and indulges himself with a piece of fish or chicken once a week. But the success of the diet, and his liberation from diet pills, has given Pincay a new sense of peace. "I take things a lot easier now," he said. If I make a mistake, I don't worry about it."

The changes in him may have helped make Pincay a more cool, calculating jockey. At least, he came from California to New York this fall with a well-established reputation as a "physical" rider, as the most powerful finisher in the country. But he has demonstrated that his patience, his judgement and his tactical sense are as formidable as his ability to punish a horse in the last sixteenth of a mile.

In an era when almost all riders want their horses to show speed and get a good position, Pincay is a throw-back who can wait and wait and wait till the last excruciating moment to make his move. The announcer at Adueduct occasionally has to interrupt his stretch call in mid-sentence because a Pincay horse has come from out of nowhere and flown into the lead in a matter of seconds.

Pincay's most dramatic display of this kind of patience came before a nationwide television audience in the Woodward Stakes at Belmont. His mount, Affirmed, was leading on the stretch turn when his two prinicpal rivals moved up on the outside -- and swooped by him. The crowd let out a collective gasp: the champ was beaten!

In fact, Pincay was just waiting. "I know the horse and I know when he's trying his best. When the other horses started to run, he wasn't ready. He wasn't responding, wasn't accelerating on his own. If you push a horse before he's ready, he can get confused, and it will take something out of him."

So instead of imposing his will upon Affirmed, he waited until he felt that Affirmed was ready. When that moment arrived in the stretch run, Pincay started pumping, moving in perfect sychronization with the animal's strides, and drove him to an electrifying come-from-behind victory.

"That was one race I was proud to ride," Pincay said. "If I hadn't ridden him that way, he probably would have gotten beat."

You could watch a thousand races without seeing a horse ridden the way Pincay rode Affirmed that day. An ordinary jockey wouldn't have dared to do it, even if he thought it was right. Pincay's ride was the sort that a jockey can deliver only when he possesses the unshakable self-confidence that comes from success, and only in one of those periods when his every move is magic. CAPTION: Picture, Jockey Laffit Pincay, Jr., left, whose mounts are nearing $8 million in winnings this year, challenges Spectacular Bid coming down stretch of Kentucky Derby. AP