It would be hard to guess, from his decision to keep Kentucky Derby winner Gato del Sol out of Saturday's Preakness, that trainer Eddie Gregson once studied to be a historian.

His rationale for bypassing Pimlico and going to New York to await the Belmont Stakes suggests that Gregson failed to learn some important lessons from Triple Crown series of the past. Even worse, he has committed the cardinal sin of his once-intended profession. He has accepted a popular myth that contradicts historical facts.

Gregson wants a fresh horse for the Belmont Stakes and does not intend to run Gato del Sol between now and June 5. But decades of Belmont results show unequivocally that this approach is wrong. Horses benefit greatly from a prep race a week or two before the Belmont; they need that conditioning to go 1 1/2 miles. They don't win that demanding event after a five-week absence from competition. If Gregson accepted the fact that Gato del Sol needed to run some time between the Derby and the Belmont, he might as well run him at Pimlico, where he could could earn $200,000 while engaging in his tuneup.

But Gregson insisted, "The Preakness is the wrong race for this horse." The owners agree with him. A spokesman for co-owner Arthur Hancock explained: "Linkage is there at Pimlico with those sharp turns and the Preakness is a sixteenth of a mile less than the Derby. The trainer knows the terrain there and his advice is that the Belmont is the best race for Gato del Sol."

Most racing fans also would accept the premise that Pimlico's sharp turns and speed-favoring tendencies, as well as the 1 3/16-mile distance of the Preakness, should hinder a stretch-runner like Gato del Sol. So it is a little surprising to study the recent history of the Preakness and find that the results flatly contradict this popular notion.

The Preakness has not been dominated by speed horses. In fact, only one horse in the last 20 years--Bee Bee Bee in 1972--has led all the way to win it. The Belmont Stakes is a far more speed-favoring race.

And even though the sharp turns hinder stretch-runners who make wide moves in ordinary races at Pimlico, they don't seem to make much difference in the Preakness. Pleasant Colony circled the field on the turn to win in 1981. Nobody will ever forget the way Codex drifted wide into the path of Genuine Risk the year before. Spectacular Bid swooped around the field in 1979.

The principal difference between the Preakness and the Derby is that horses don't come from so far behind at Pimlico; they don't because the composition of the fields is usually much different.

The Derby often is heavily populated by speed horses who have little chance to win but who will set a fast pace; the field usually will be strung out behind them. But the owners and trainers of such horses usually come to their senses after the first Saturday in May and, as a result, the Preakness field is much less cluttered with speedsters who don't belong. The pace usually is slower and so the stretch-running types must stay closer to the lead.

Last year, for example, Pleasant Colony dropped some 20 lengths behind an insane speed duel in the Derby; in the Preakness he lay about a half-dozen lengths behind Bold Ego's moderate pace. Spectacular Bid and Secretariat similarly modified their styles and stayed closer to the pace to win the Preakness.

Only once in recent years, when Bee Bee Bee beat Riva Ridge and Key to the Mint, could one argue that Pimlico's idiosyncrasies contributed to an "untrue" Preakness result. And that upset probably was due most to the sloppy track. The Preakness is an honest race generally won by the best horse. Perhaps that is what Gregson fears.