In a year when a horse can win the Kentucky Derby after training in Arkansas, historical precedents evidently don't count for much.

So perhaps another rule of Triple Crown training is about to be violated: the one that says a horse should run in the Kentucky Derby if he wants to win the Preakness.

Horses who skip the Derby and come into the Preakness "fresh" are usually spotting their rivals too much of an edge in conditioning. Plenty of horses have tried this method of preparation, but in the last two decades only three have succeeded--Bee Bee Bee in 1972, Codex in 1980 and Aloma's Ruler in 1982.

But this year could be an exception to the rule, because an unusually large number of good 3-year-olds are taking unorthodox routes to the Preakness. Most of them are running today in prep races at Pimlico, Aqueduct or Keystone.

Six colts are entered in the Preakness Prep, and at least one of them, Assault Landing, has shown the potential to be a top 3-year-old. He won the one-mile Gotham Stakes at Aqueduct last month and would have been the favorite in the Wood Memorial, but he suffered a foot injury that set back his training. Now the Laurel-based colt, trained by Charles Hadry, is fit again. Since three of his rivals today are speed horses--Noble Home, Dixieland Band and Bet Big--the 1 1/16-mile race should be made to order for his stretch-running style.

The $75,000 Withers Stakes at Aqueduct has attracted three horses who could conceivably be important factors in the Preakness.

Megaturn is unbeaten in four career starts, and he has impressed New Yorkers with his powerful finishes against lesser competition. Trainer Richard Nieminski prudently bypassed the Derby, knowing the colt didn't have the necessary seasoning, but he will probably bring Megaturn to Baltimore if he runs well today.

He will face serious competition from Intention, a colt trained by Billy Turner who has won both his starts this year, and from I Enclose, who remains something of an enigma. I Enclose looked like one of the best 2-year-olds in America last fall and had been widely considered a Derby contender, but he never showed up in a race until Monday, when he tired and finished fourth on the grass at Aqueduct. Trainer Eddie Kelly is a shrewd veteran, however, and if he runs I Enclose five days after this mediocre performance, he probably means business today.

In Philadelphia, 11 3-year-olds have been entered in the $25,000 Keystone Stakes, and one of them, Deputed Testamony, is trying to redeem himself and earn a berth in the Preakness. Deputed Testamony looked very impressive when he won the Federico Tesio Stakes at Pimlico last month, but he flopped dismally in the Blue Grass Stakes.

The outcome of today's prep races will have a significant bearing on the way the Preakness is run. Sunny's Halo and Desert Wine were able to run one-two most of the way at Churchill Downs because there was little speed to pressure them. They might have the same luxury next Saturday, and if they do Sunny's Halo will be very difficult to beat again. But if Bet Big, Intention or Noble Home earns a berth in the Preakness, Sunny's Halo will at least be forced to work harder.