SARATOGA SPRINGS, N.Y. -- After racing officials here received a tip that Alysheba would be treated with an illegal drug before Saturday's Travers, reports of the incident put into headlines a word that has been whispered around American racetracks for years: endorphins.

The New Jersey state police had passed the information about Alysheba to Saratoga's stewards, who ordered the colt's barn guarded Saturday afternoon. Naturally, nothing happened. Nobody was going to be wielding a hypodermic needle near the favorite under the circumstances.

But the report had credibility, partly because the New Jersey police have proved to be astute investigators of the sport, and partly because the substance they said would be used is the most talked-about illegal drug in the sport today.

In fact, nothing has posed as difficult a problem for chemists trying to detect illegal drugs as endorphins do. They may be indistinguishable from substances that occur naturally in the body.

Mankind has known for centuries that morphine and other narcotics suppress pain, but it was not until 1975 that scientists learned just how and why they work. Solomon Snyder, a professor at Johns Hopkins, discovered that the brain manufactures substances called endorphins to help the body cope with pain.

If somebody punches you in the nose, your brain quickly manufactures these molecules. If you jog five miles, endorphins are released (an explanation for the so-called "runner's high.") The endorphins are broken down quickly, too, because the body doesn't want them hanging around when they're not needed.

The discovery of endorphins created a whole new area of scientific inquiry. Endorphins could be made synthetically. And they attracted the attention of the racing world -- as discoveries about pain-relieving drugs usually do. Synthetic endorphins would be potent narcotics; they would disappear from the horses' systems quickly; and they would be virtually impossible to detect.

Dr. Thomas Tobin, a professor at the University of Kentucky and author of "Drugs and the Performance Horse," conducted some of the earliest tests with endorphins and didn't find them especially effective. He found that if they were given intravenously they didn't enter the brain fast enough; he had to inject them directly into the brain, through the base of the skull, to get limited results. "As far as I know," Tobin said, "the biggest effect of endorphins in racing has been to give rise to a lot of rumors."

But since Tobin's early experiments, many new endorphins have been synthesized and, surely, many trainers and veterinarians have tried countless variations of ways to administer it. The phenomenal success of certain trainers, whose horses seem to defy the laws of nature and who have never been caught for a drug "positive," has suggested that potent narcotics of some type have been in common use.

When the rumors about Alysheba surfaced, there were some suggestions in the media that endorphins might be a substitute for the Lasix that the colt was not permitted to use legally in New York. Tobin said no. "To the best of my knowledge," he said, "that's a whole different bag. Endorphins are associated with pain suppression. They are agents that affect the nervous system."

He did say, though, that there are some very effective Lasix substitutes in existence, including one which is 20 times stronger than Lasix and thus requires 1/20 of the dose, making it very hard to detect.

But nothing could be harder to detect than endorphins, because they occur naturally in the body. If, indeed, they are be used effectively on horses, the only way to stop the drug would be to do what Saratoga officials did: guard the horse before the race.