After winning the Kentucky Derby, Gato del Sol came here to await the Belmont Stakes because trainer Eddie Gregson thought his stretch runner is the type of horse who would be much better suited to this race than to the Preakness.

In one small respect, Gregson was correct: the Belmont, more than either of the other Triple Crown events, favors a particular type of horse. But in the crucial respect, he was wrong. Gato del Sol is not the right type.

He will not win on Saturday.

The history of the Belmont indicates, unequivocally, that a horse must have the right kind of conditioning to win at 1 1/2 miles. And that conditioning comes from a recent race. Even horses who ran in the Preakness three weeks earlier find themselves at a significant disadvantage against rivals who have had a prep race in the previous week or so.

"That three weeks puts you in a real bad spot," said Calumet Farm's trainer, John Veitch. "The Belmont is close enough that you can't train real hard, and people are very afraid to overtrain. But the Belmont is a demanding race, and a prep race six to nine days beforehand really gears horses up and gets them dead fit."

With an edge in condition, inferior horses can beat superior rivals. Last year, Summing won the Pennsylvania Derby and came back 12 days later to upset Pleasant Colony and the rest of the colts who had run well in the Preakness. Temperence Hill came into the 1980 Belmont seven days after a prep race and scored a stunning victory. In 1979, Coastal had the advantage of a recent race and upset the great Spectacular Bid.

Nobody appreciated the importance of a prep race for the Belmont more than trainer Elliott Burch. Three times, Burch lost the Preakness--with Sword Dancer in 1959, Quadrangle in 1964 and Arts and Letters in 1969. Each time, he ran his horse in the one-mile Metropolitan Handicap on Memorial Day. And each of the horses came back to win the Belmont, defeating the rivals who had beaten him in Baltimore.

If the three-week layoff before the Belmont is a disadvantage that only outstanding horses can surmount, a five-week layoff before the race ought to be insuperable. No horse has successfully done what Gato del Sol is trying to do in at least 50 years. The last Derby winner who tried it was Count Turf in 1951. He lost the Belmont by 20 lengths.

Gregson's decision to point for the Belmont was, of course, based on Gato del Sol's running style. In his races at 1 1/8 miles, the gray colt's rallies had fallen short. In the 1 1/4-mile Derby, he managed to come from last place and overtake all 18 of his rivals. So it makes sense that 1 1/2 miles will suit the stretch-runner even better. "The Belmont is the race I always felt would be his best go," the trainer said. "The win in the Derby only makes me more confident."

This is familiar reasoning. Whenever a 3-year-old makes an impressive stretch run before the first Saturday in June, people will say that he looks like a Belmont horse; they assume that in the extra distance of the race he will continue to accelerate while his rivals are faltering.

The assumption is frequently wrong. The Belmont is not the Kentucky Derby with another quarter-mile tacked on at the end; it is a different sort of race entirely.

The Derby and the Preakness are often won by horses who make one bold, decisive move (as Pleasant Colony and Spectacular Bid did). But one burst of speed usually will not enable a horse to seize control of a 1 1/2-mile race. The Belmont is more often won by horses who have some speed and run an even-paced race.

Five of the last 10 Belmont winners have led all the way. Most of the horses who have come from behind have done so not with a whirlwind finish, but with an even-paced performance. Last year, Summing ran his six quarter-miles in 24 seconds, 24 4/5, 25 2/5, 25 1/5, 24 3/5 and 25. Only two horses in the last decade--Temperence Hill and Little Current--have fit the stereotype of the slow, stretch-running Belmont winner.

Gato del Sol has the wrong style for the Belmont. He has the wrong kind of preparation. He is the wrong horse, period.