The ugliest story of the 22nd Olympics began in a bathroom in the basement of Seoul's track-and-field stadium. There, on Sept. 24, a smallish man with a fabulously muscled body and rage-filled eyes had to perform the indignity of champions. A master of explosive, almost inexplicable starts, he had already propelled his body down the 100-meter track faster than anyone before. Now his legs had ceased churning, he had relinquished the flag of his adopted Canada, which he had waved around the stadium, and the applause for the seemingly guileless sprinter who had dethroned the all-too-sleek Carl Lewis had died. Only a urine sample stood between Ben Johnson and a nightlong celebration for the happiest day of his 26 years.

It took just 9.79 sec. to run the 100, but it took Johnson nearly an hour and six cans of low-alcohol beer to fulfill his requirement. At the Doping Control Center of the Korea Advanced Institute of Science and Technology, it took twelve hours more to assay the day's samples, to run them through the mazy innards of the lab's instruments. When the last sample left the hair-thin glass tubes of the gas chromatograph and the mass spectrometer, where all molecules have their fingerprints taken, just one positive result had turned up.

The result was reported to Prince Alexandre de Merode, the Belgian chief of the International Olympic Committee's Medical Commission, and he then checked to determine whose sample it was, for it was identified only by number. Frantic meetings ensued, and a second portion of the original sample, which had been stored in a locked refrigerator, was tested. The results were the same: Ben Johnson, the fastest man on earth, had cheated.

After Canadian officials were notified that he had tested positive for the anabolic steroid stanozolol, a substance that is supposed to help build lean muscle mass, they hustled the Jamaican-born sprinter out of Olympic Village, the cockpit of his glory, and checked him into a Seoul hotel under an ignominious pseudonym. There, at 3:30 a.m. on Tuesday, Carol Anne Letheren, chef de mission of the Canadian delegation, stripped Johnson of the medal he had already given to his mother. ''He was in a state of shock,'' said Letheren. ''He still did not comprehend the situation.'' A few hours later he was bound for New York, a runner who had stumbled into a future stained with disgrace.

In Canada, a country that was delighting in its first gold medal of the Games, outrage abounded. Canadian Sports Minister Jean Charest announced the draconian penalty of banning Johnson from ever representing Canada on a national team again, calling the incident a ''national embarrassment.'' Many saw the sprinter as pitiable, and some, like I.O.C. vice president Richard Pound, believed he had been duped as well as doped, saying, ''Johnson probably wouldn't know what a steroid is.'' But across Canada spread a sense of bewilderment and anger.

Around the world, Johnson's disqualification suddenly riveted public attention on the decades-old problem of performance-enhancing drug use with an altogether new intensity. By week's end the total of ten drug-related disqualifications in Seoul was close to the 1984 figure. But many thought: If this world-record holder would risk detection, everyone must be doing it. Spectators felt deceived and non-using athletes felt gypped. Overnight the Olympics became clouded, suspected of being an unholy chemistry competition rather than the glorious alchemy of will, talent and training that is its ideal.

The doctor who allegedly gave Johnson the steroids, George M. Astaphan, did not realize that stanozolol can now be detected. Stanozolol was hard to observe in the 80s -- a fact that may explain why three of the Seoul disqualifications were for that particular steroid. There was no question about the veracity of the test: in Johnson's sample, said Jong-Sei Park, chief of the Olympic drug testing lab, ''we saw the stanozolol itself and the breakdown products'' it leaves in the body.

Confirmation that Johnson had been using the drug for some time, at least several months, came from the very low levels of natural testosterone in his urine sample; the glands that produce the hormone shut down when the system is flooded with the synthetic chemical. Apparently Johnson made it to the Games because of a stroke of luck in the Canadian Olympic trials: two of the top three finishers are tested after each event, and Johnson drew the lucky straw that exempted him.

With the results of Johnson's test widely accepted, attention focused on how he had been doped. At the center of the controversy was Dr. Astaphan, a general practitioner on the Caribbean island of St. Kitts. Astaphan has been associated with Johnson for more than five years, and the sprinter spent several weeks this summer on St. Kitts, purportedly being treated for a hamstring pull. Astaphan denied the reports that he gave Johnson stanozolol but did say he gave him therapeutic corticosteroids and subsequently notified the I.O.C. The doctor also became the subject of intense scrutiny. York University officials, according to a Toronto newspaper, were looking into claims that athletes training at the university had bought steroids from Astaphan. The College of Physicians and Surgeons of Ontario announced it would investigate Astaphan's medical practice. But Ben Johnson was not talking. Before leaving Seoul, he denied knowingly taking steroids. On the flight back he wept, and when he finally arrived in Canada, he retreated to his mother's suburban Toronto home, where he lives. The well-built edifice of endorsements that had been erected for him collapsed overnight; he stands to lose an estimated $8.2 million. The only light in his personal tunnel, and a lurid one at that, came when Canadian and American football teams announced their interest in his services. The Canadian government promised an inquiry. Nothing less, it seemed, would explain the story of the man who, advertently or not, brought the 1988 Olympics to their highest and lowest moments.

Johnson would later claim that shortly before running his gold winning race he was the unwitting recipient of steroids. According to his story, he was getting ready in a locker room where several of his friends were injecting steroids. Johnson turned down their offers to shoot up. While on his way out to race, Johnson slipped on a wet towel and feel on a hypodermic needle filled with steroids.