After his brilliant performance in the Kentucky Derby Saturday, Spend A Buck is being hailed as the bright new star of American racing.

It's a fickle game. Only 48 hours ago, before his third- place finish at Churchill Downs, Chief's Crown was being hailed as the bright star of American racing.

Spend A Buck is probably the more gifted horse; he has the combination of blazing speed and stamina that every thoroughbred breeder dreams of creating. But the colts are similar in this respect: Both made their reputations and scored their great victories under such favorable conditions that they could hardly fail. When Chief's Crown had to cope with a measure of adversity for the first time as a 3-year-old, his limitations were exposed on Saturday. The same fate probably awaits Spend A Buck, sooner or later.

There is no surer way to make a bad horse look good, or to make a good horse look great, than to put him in a field where he is the only front- runner and to let him control the pace from start to finish. Almost all of the top 3-year-olds made their reputations this spring in such a way. Chief's Crown led all the way to win the Flamingo and the Blue Grass Stakes; Rhoman Rule coasted to victory in the Everglades; Eternal Prince wired the field in the Wood Memorial; Spend A Buck was the only front-runner in the Cherry Hill Mile and the Garden State Stakes.

The Kentucky Derby figured to be the genuine test of all of them, since nobody was going to have such an advantage. Spend A Buck and Eternal Prince, the fastest horses in the field, were going to keep each other -- and everybody else -- honest.

But this head-to-head competition didn't materialize, and the whole Derby became somewhat of a disappointment, because of Eternal Prince and/or jockey Richard Migliore.

"Either the horse or the jockey wasn't sharp," trainer Butch Lenzini said this morning. "One or the other wasn't ready at the start."

Migliore said Eternal Prince was distracted by the crowd and all the hoopla at Churchill Downs, but the jockey himself may have been intimidated. When the gate opened, he was tentative; he never made any aggressive effort to drive his horse to the lead, even though that was the intended strategy and the only way Eternal Prince had a chance to win.

After the field had gone an eighth of a mile, Lenzini exclaimed, "Where the hell's he at?" Caught in traffic, his colt never got into competition, and Spend A Buck was in front by himself after running the first quarter-mile in a slow 23 seconds.

If only the betting windows were still open! Spend A Buck already had shown what he could do under such conditions. After a first quarter in :23 at Garden State, he had run 1 1/8 miles just slightly slower than Secretariat's world record for the distance. So it was no surprise, no revelation about his capabilities when he ran within four-fifths of a second of Secretariat's Kentucky Derby record.

The last impetuous front-runner to win the Derby was Bold Forbes in 1976. Spend A Buck probably has more talent than Bold Forbes, but horses with their running style typically have similar limitations. They can win all-out, head-and-head battles at distances up to a mile, but when they go farther they must be able to control the pace to be effective. (When Bold Forbes got into a duel with Honest Pleasure in the Preakness, both of them collapsed.)

Spend A Buck still has not run a race beyond a mile in which he has been subjected to early pressure. If he could prevail under such conditions -- say, after being outrun for the lead by Eternal Prince in the Preakness -- he may be considered a genuinely great racehorse. Until he faces such a test, we can hail him for his brilliant speed and stamina but reserve final judgment on his total capabilities.