One of the special qualitites of throughbred racing is that it offers a chance to relive or recapture the past. Whenever a great horse ends his career, people can look to his sons and daughters, his brothers and sisters, and hope they will emulate his feats.

More often than not, such hopes go unfulfilled, but even the most realistic owners and trainers cannot help entertaining them. And so when the man from Churchill Downs came to Laz Barrera's barn at Santa Anita to take nominations for the Kentucky Derby, the trainer pointed at a chestnut colt and said, "That is the Derby winner."

The colt's name was Silent Fox, and with the Derby only 2 1/2 months away he had still not run in his first race. But Barrera's exuberance was understandable, because Silent Fox evokes the most shining moments in his career. A son of Exclusive Native and Won't Tell You, he is a full brother to Affirmed, whom Barrera trained to win the Triple Crown and the horse of the year title. Barrera has had special hopes for him ever since he got a phone call from a Texas oilman named E.C. Johnston, who told the trainer he had a horse in whom he might be interested.

Johnston is not a prominent horse owner, but in the summer of 1977 he made one deal worthy of the sport's sharpest wheeler-dealers. He had been impressed by Affirmed's performances in his first races as a 2-year-old, and learned that his dam was entered in a sale of breeding stock in Arkansas. So Johnston decided to try to buy the mare privately.

"We got in the car and drove to Arkadelphia, Ark., and it was raining like hell," he recalled. "The mare was standing out there in the rain with a filly at her side and she looked so bad that my wife said, 'You don't want that mare.' I told her that we had to look at this from some other angles." Johnston bought Won't Tell You for $42,500, and no oil well he ever drilled gave him such a nice return on his investment. When Affirmed became a champion, his mother became a seven-figure property.

Johnston sent her to Spendthrift Farm to be bred back to Exclusive Native, and the farm manager suggested that he contact Barrera to train the horse. "Oh, Barrera wouldn't want to fool with me," Johnston said. "Maybe not," the farm manager said, "but he'll want to fool with this colt."

From the outset, Barrera liked what he saw. Silent Fox trained swiftly last fall, but he hurt his shins and delayed his career debut. This winter he not only trained like a good horse, he acted like a good horse. "He does a lot of things like Affirmed used to do," Barrera said. "He does what you ask him. If you want him to work slow, he'll go slow. If you want him to work fast, he'll go fast. He'll lay down and sleep a lot, and that's a very good sign, because he's saving energy."

Of course, Barrera and every other trainer have had horses who do everything right in the mornings and then disappoint them in the afternoons. But when Silent Fox made his racing debut at Santa Anita, he may even have exceeded his trainer's and owner's expectations.

He seemed to be facing an insuperable disadvantage when he drew the No. 1 post position, because the inside part of the track was very deep and no horse had been able to run well on the rail all day. But he stayed on the inside and rallied to win by a length over a decent field of maidens, running as fast as seasoned 3-year-old stakes horses did later in the afternoon.

Now Barrera could start to speculate about the Kentucky Derby and not be thought utterly unrealistic. Ideally, he said, he would like to run Silent Fox in an allowance race, then a minor stakes, then the Santa Anita Derby. From there he would go to the Blue Grass Stakes and then to Churchill Downs. At this stage all of this is still a long-shot proposition. But Silent Fox has at least given Barrera no reason to abandon his hope that he is about to relive the glorious past and train another Affirmed.