Many American racing fans suspect that illegal drugs pervade the sport. The basis of this notion is the ability of certain trainers to improve horses phenomenally.

Bettors at tracks across the country can cite horses whose performances defy handicapping logic. One such animal, A One Rocket, belongs in the Hall of Fame of training miracles. His overnight transformation was so outlandish that it set in motion a series of events altering the sport in New York. The legacy of A One Rocket will be felt Saturday at Belmont Park, when all of the entrants in the Breeders' Cup will be subjected to unprecedented scrutiny.

Since May, all horses racing in New York have been required to enter a security barn six hours before they race. There they are placed under close surveillance, and private veterinarians cannot enter their stalls. While the effect of the system can't be measured exactly, anecdotal evidence suggests that the security barn has stopped much of the cheating that has plagued racing in the state.

Over the years, many trainers in New York have emerged from relative obscurity to perform extraordinary feats and compiled winning percentages that dwarf the records of legendary horsemen. Last winter the most conspicuous success was Gregory Martin, who was winning with more than 30 percent of his starters. On Dec. 13, Martin claimed A One Rocket out of a $7,500 claiming race that the gelding won by less than a length, earning a modest Beyer Speed Figure of 75.

Five days later Martin entered his new acquisition in a $12,500 claimer, and he ran away to a 10-length win, earning a Beyer Speed Figure of 103 -- a stupefying improvement. At the time of this performance, a new chief executive had taken the helm of the New York Racing Association. Charlie Hayward had previously been president of the Daily Racing Form, and he was a longtime fan who questioned such form reversals. He printed out the past performances of two Martin-trained horses and asked stewards if they saw anything suspicious. When the stewards said no, Hayward asked, "Would you mind if I get Greg Martin in and talk to him?"

Hayward summoned the trainer, and listened skeptically to his explanation that his horses' improvement was because of treatment with an ulcer medication. It is unusual for a track executive to grill a trainer under such circumstances, and some people might have wondered if NYRA's new CEO harbored the same mentality as the paranoid horseplayers in the Aqueduct grandstand. But within a month, it was evident that his suspicions were justified. A federal investigation into a gambling operation focused on A One Rocket, who reportedly had been treated with an illegal "milkshake" -- a mixture of bicarbonate forced into his stomach through a tube -- before his Dec. 18 victory. And the feds were throwing the book at the offenders. Martin was one of 17 people charged and could face a maximum of 25 years in prison.

While many racetracks have turned a blind eye to concerns about cheating, NYRA couldn't ignore this headline-making scandal. Its leadership was determined to act. Peter Karches, co-chairman of NYRA's board of trustees, had already been championing the idea of a security barn, and Hayward favored aggressive action, too.

NYRA instituted testing for milkshakes in February, and with the opening of Belmont Park in May it put the security barn into operation. Some trainers complained about the disruption to their horses' pre-race routines, but Hayward answered that it was no more disruptive than shipping a horse from Aqueduct to Belmont, which is routinely done. One prominent trainer told Hayward: "Our compatriots got us into this problem. What do we expect?"

Bettors scrutinized the results for the effects of the security barn, looking for trainers who abruptly stopped winning because of the surveillance. The evidence was subtler than that because some of the suspects have such large powerful stables that they'll win plenty of races under any circumstances.

But after following the races at Belmont and Saratoga since May, I have came to this conclusion: The overnight transformations of horses that appear to be the surest signs of cheating -- a la A One Rocket -- are much rarer than in the past. In my opinion, only two trainers are conspicuously beating the system. For the first time in more than a decade, I felt that I could handicap and bet in New York without asking, in almost every race, "Who's got the juice?"

Hayward shares the opinion that the security barn has been effective but not foolproof. "I don't pretend that the barns have stopped everyone," he said. "You look at the past performances and that's not the case."

The new system will surely be a factor Saturday. Although the Breeders' Cup has its own security rules -- horses must be on the grounds 24 hours before the races -- the pre-race security at Lone Star Park last fall was widely criticized. Horses weren't under close surveillance in the crucial hours before they raced, and cynics wondered afterwards if this negligence affected certain results. But for the six hours before they race Saturday at Belmont, the nation's best horses will be under scrutiny, and it is very likely that the races will be won by the best horses -- not the ones whose trainers and veterinarians possess magical elixirs.