Fourteen horses have been entered in Saturday's $50,000 Derby Trial Stakes, for a variety of reasons. Some are using it as a tuneup for the Derby itself; others will be trying to earn a berth in the Churchill Downs classic. Some are here because their trainers have planned their campaigns meticulously; some are here for no rational reason at all.

Trainer Woody Stephens has a good reason to believe that giving a horse a race over the Churchill Downs track is a smart tactic; that is the way he won the centennial running of the Derby with Cannonade in 1974. So today he will start two colts, Chumming and Caveat, in the Trial. Neither has quite lived up to early-season expectations.

But the Stephens entry is expected to be cofavored with Pax in Bello, whose presence remains a mystery. The colt has not had a 1 1/8-mile race this year, and trainer Steve Jerkens sent him from Florida to New York for the Wood Memorial.

But then Jerkens announced, with no cogent explanation, that Pax in Bello would pass the Wood and go to Churchill for the Trial--even though a one-mile race hardly seemed to be what he needed. Suspicions linger that something may be physically wrong with the colt.