Copelan, who was considered the favorite for the Kentucky Derby two months ago, will not run in Saturday's race.

Owner Fred Hooper said his colt suffered a cut on his right foreleg when Marfa swerved in front of him in the stretch run of the Blue Grass Stakes at Keeneland last week. He will be sent to Florida to recuperate.

Before this mishap, however, Copelan had been suffering from a chronic lack of stamina. He was tiring in the Blue Grass, just as he had tired in all of his longer races, and he was clearly unsuited to the 1 1/4-mile Derby distance. So if the report of his cut leg was not a face-saving device, it was at least a timely injury.

With the defection of Copelan and a few others, it seemed possible that exactly 20 horses would be entered in the Derby. Thus, Churchill Downs would not have to invoke the rule limiting the field to the 20 entrants who had amassed the greatest career earnings.

The defection of such lightly regarded horses as Noble Home and Le Cou Cou opened the way for one legitimate contender to get into the field. High Honors had finished fast to be third in the Wood Memorial at Aqueduct, but the purse money he earned that day raised his career earnings to only $46,940, and trainer Lou Rondinello was resigned to his exclusion from the Derby. Now he is on his way to Churchill Downs.

In another development, Explosive Wagon was treated for respiratory problems today but appeared to recover. Trainer Gene Norman said he was certain the horse still would race Saturday.