AS two of the most powerful figures in international sport united yesterday to call for an inquiry into allegations of drug abuse by American Olympic champions, it emerged that the key witness will be unavailable.

Robert Helmick, chairman of the US Olympic Committee during a period in which it is claimed that dozens of dope cheats escaped conviction, died hours after allegations were published earlier this week.

Dr Wade Exum, the director of drugs control at USOC from 1991 to 2000, made it clear that he would reveal 30,000 pages of what he claims are incriminating documents if he lost a court action for racial discrimnation against the organisation.

That case collapsed on April 9. Helmick subequently had a stroke, and died on April 15, the day on which the Exum files were made public.

Among 114 cases of positive dope findings to go unpunished were three for a stimulant in cold medication used by the 20th century's greatest athlete, nine-times Olympic champion Carl Lewis.

Lewis had matched the 1936 Berlin Olympic champion, Jesse Owens, by winning gold in the 100, 200 and 4 x 100m relay, plus the long jump, in Los Angeles. Banning him from the 1988 team in Seoul, denying his right to defend, would have humiliated America, and damaged sponsorship of the team, for whom he was an icon.

Helmick left in disgrace during his sixth year as USOC president, in September 1991, denying reports that he had accepted nearly $300,000 ''trafficking on his Olympic positions.'' He was later exposed. As a member of the IOC, Helmick was entitled to visit Olympic host candidate cities. When Birmingham was challenging Barcelona for the right to stage the 1992 Games, Helmick cashed in his first-class air fare without ever visiting the city.

It was during his tenure that Lewis and company escaped censure which would have changed the face of sporting history. Tellingly, Exum's predecessor, Dr Robert Voy, resigned for similar reasons.

Exum's dossier also shows that 1988 Olympic champions Joe DeLoach (200m) and Andre Phillips (400m hurdles) showd positive for stimulants. So, too, did tennis player Mary-Jo Fernandez, who won medals in 1992 and '96. Each received letters of warning, rather than the ban which international rules demanded.

USOC deny wrong-doing, and claim Exum was attempting to secure a $5.5m settlement in return for his silence.

When the case collapsed, Exum lodged his documents with the magazine Sports Illustrated and the Orange County Register, a newspaper which has published details this week.

Istvan Gyulai, secretary of the International Association of Athletics Federations, and Craig Reedie, a member of the International Olympic Committee, said yesterday that investigation of the allegations seemed appropriate.

Guylai said: ''I am always suspicious when someone has done a job for many years, and then later comes out with something like this. When the person has left, it does not have the highest level of motivation.

''If he had done it while in post, I'd have said this was a tough guy, yet if these allegations are proved to be facts, and that's a very big if, then the athletics world, and the sports world, needs an investigation.''

Reedie, chairman of the British Olympic Association and a retired Glasgow financial consultant, said: ''I agree with Istvan, but I agree with him as much for Carl Lewis as anybody else. If these allegations are not correct, the sooner they are cleared up, the better for those names and reputations.''

The 1988 Olympic 100m final now assumes even more infamous proportions. Ben Johnson was banned after it was proved that his victory had been steroid fueled. Lewis should not have been there and Linford Christie, promoted to bronze, ''was given the benefit of the doubt'' in a vote on whether to ban him over a stimulant he used. The delicately-boned Calvin Smith, world 200m record holder, who finished fourth and was awarded bronze, is perhaps the man who should have been king. The fifth and seventh-placed men, Dennis Mitchell and Desai Williams, were subsequently implicated in drugs.

Smith was somewhere in his home state of Alabama, but could not be traced yesterday.

Two years ago, Exum said on TV: ''I believe that we sent athletes to every Games that have been using performance-enhancing drugs."

Potential disclosures are legion. Cyclist Greg Strock rode for the US in the same year as six future Olympic athletes, including Tour de France winner Lance Armstrong. A prodigy at 17, Strock fell ill. It was thought he had Aids, then lymphatic cancer. It turned out to be a defective immune system. Strock quit and went to medical school. While studying steroids, he was alerted about Exum's files, and his suspicious were further aroused.

He was given pills and injections which he believes to have been banned drugs. USOC and USA Cycling deny this, but Strock has proceeded with an action against them. Coach Chris Carmichael, still Armstrong's mentor, is named in court documents. That case remains undecided.

''I believe we were being doped. We were being groomed,'' claims Strock.