As principal contenders have been dropping out of the race, mediocre 3-year-olds have been coming to Churchill Downs by the planeload to take a shot at winning the 108th Kentucky Derby.

From New York today came four colts--Wolfie's Rascal, Majesty's Prince, Reinvested and Mid-Yell--whose trainers belatedly decided to enter the Derby.

Trainer John Mabry informed track officials that Real Dare would be shipped here Wednesday. He evidently saw some virtues in the gelding's 27-length loss in the Louisiana Derby that were not apparent to other witnesses.

Trainer Eugene Jacobs decided today that he would enter Cut Away along with stablemate New Discovery, even though the colt hasn't run for six weeks (and didn't run too well then). "He'll help set the race up for New Discovery," Jacobs explained. The horse Cut Away is supposed to set it up for has won once in his career and finished eighth in the Blue Grass Stakes last week.

The influx of these undistinguished horses almost insures that Churchill Downs will have to invoke the rule limiting the Derby field to the 20 entrants with most career earnings. At least 23 horses are now considered Derby candidates, and the trainers of those at the bottom of the list will not know until Thursday whether they will get a chance to run.

The Derby has always attracted some horses who don't belong in the race, whose owners and trainers have come here for a lark, but such animals appear to be in the majority on Saturday. After Timely Writer was knocked out of the Derby by an illness, Linkage bypassed the race to prepare for the Preakness and Hostage fractured a sesamoid bone in a workout, just about anyone with an ambulatory 3-year-old thoroughbred figured he might have a chance.