Philadelphia ? The smoking gun was a dripping syringe, and sports as we know them may never be the same.

The syringe, sent to the U.S. Anti-Doping Agency (USADA) by an anonymous track-and-field coach, led to an investigation into a brand-new designer steroid.

The big question is where it will lead. Already, there are very real questions about the integrity of the Olympics, the World Series and several of the greatest single-season performances in the history of major league baseball. Oh, and the NFL is just beginning its own investigation.

“What we’re looking at here is the flower in the bud stage,” said Charles Yesalis, a Penn State professor and nationally recognized expert on performance-enhancing substances. “It might be a dead blossom, but I think a lot of people are feeling very nervous right now.”

It sounds melodramatic, but this could be fair play’s last stand. The sheer breathtaking science in this case makes it a sort of crossroads in the battle against cheating.

The new drug is called THG (for tetrahydrogestrinone), a form of steroid that has been manipulated at the molecular level by chemists to escape detection by known blood and urine tests.

It took the USADA experts weeks to figure out a way to test for THG after the syringe arrived, and that was with access to a sample of the stuff. So, you have to wonder, what else is out there that authorities don’t know about? If there is one product designed to beat the testing equipment, you just know there have to be more. Maybe many more.

“When you think about the big scandals of the last few years, the one constant is that testing has very little to do with catching anyone,” Yesalis said. “In this case, a coach sent the drug to the lab. (USADA’s) Don Catlin, a terrific scientist, was able to identify it and reverse-engineer a test for it.”

Investigators are going after the users and the alleged maker of THG. Already, there are reports of world-class track-and-field standouts turning up positive in new tests of existing urine samples. This thing could have a profound impact on the 2004 Olympics, with American medal hopefuls missing the Games because of suspensions. The International Association of Athletic Federations said it would retest samples from the track-and-field world championships in August. That could lead to even more suspensions.

The NFL says it will add THG to its list of banned substances and test for it in the future. The league hadn’t decided whether to run new tests on urine samples. Major league baseball, as usual, doesn’t seem to want to know too much. Baseball says it won’t retest existing samples.

The man who is being investigated as the source of THG is Victor Conte, who runs the Bay Area Laboratory Co-Operative (BALCO). Based in Burlingame, Calif., just south of San Francisco, BALCO has a long list of clients for its legitimate nutrition and supplement products.

That list includes Barry Bonds and Bill Romanowski, Marion Jones and Tim Montgomery.