When top-class racehorses go through a successful campaign, their trainers often don't get much credit. Even the trainers themselves tend to minimize their own achievements, saying that it takes no great amount of skill or brains to manage a champion.

In fact, this isn't true. A man responsible for a top stakes horse has a thousand ways to go astray. If he becomes overconfident or overly cautious, greedy or complacent, egomaniacal or indecisive, if he succumbs to any other common human failing, the performance of his horse may be affected.

Anybody who wants to appreciate the difficulties and the pressures involved in training a good horse ought to watch Sunny's Halo for the rest of the season.

When the colt won the Kentucky Derby, he looked as if he might be able to dominate this weak generation of 3-year-olds all year. Trainer David Cross didn't have any previous experience handling a horse of this caliber, but he was level-headed and self-confident.

He seemed to have learned a lesson from his own mistakes last year, when he ignored an injury to his colt and pushed him into big-money races in which he was soundly beaten. Why had he done it?

Cross was candid: "Greed."

Now he had thoughtfully mapped out a 3-year-old campaign that would take Sunny's Halo to the Preakness, the Queen's Plate at Woodbine and the Swaps Stakes at Hollywood Park.

But when he encountered his first setback--the poor performance of Sunny's Halo in the Preakness--Cross seemed to lose that confidence and decisiveness.

First, he acknowledged that he would have to give Sunny's Halo a breather so he could treat and cure, once and for all, the skin rash that had plagued him all spring. The colt's performance at Pimlico seemed to confirm the fact that he needed a rest.

But then the trainer decided to send him halfway across the country to run in the Arlington Classic June 21, a race that had never been on his schedule. That proved to be a disastrous mistake; Sunny's Halo finished fourth against an undistinguished field.

But this time Cross didn't take the blame for his miscalculation. He blamed Pimlico. He said that Sunny's Halo had come out of the Arlington race with an injured ankle, but thought that the damage had occurred in the Preakness and that "the condition of the racetrack that day had a lot to do with the injury."

If that were the case, why didn't Cross notice the problem? And why did he stay at Pimlico after the Preakness and keep training Sunny's Halo on that supposedly hazardous track?

Cross was making feeble excuses, but now he accepted the fact that Sunny's Halo needed a rest. He said the colt would swim and jog as therapy, and undergo treatment with a device that sends electromagnetic charges through the injured area. He hoped that Sunny's Halo would be healthy for a fall campaign.

Five days later, Cross announced that he would ship Sunny's Halo to Monmouth Park July 8 to prepare him for the Haskell Invitational Handicap July 30. The ankle injury, he explained, wasn't really so serious.

David Cross likes to visit Las Vegas, and he has probably seen many gamblers hit a streak of bad luck, lose their composure and press their bets in a desperate effort to recoup. Now, it seems, he is behaving the same way.

Cross is a smart man and a skilled horseman, but he is discovering that managing the fortunes of a potential champion involves problems, pressures and temptations that he couldn't have imagined a few months ago.