LONDON, England -- Track and field's governing body will retest all drug samples from the recent World Championships to check whether any athletes were using a previously undetectable designer steroid.

The International Association of Athletics Federations said Tuesday it will reopen the estimated 400 samples taken during the Aug. 23-31 championships in Paris, France to search for the anabolic steroid tetrahydrogestrinone, or THG.

The drug is at the heart of a doping scandal in the United States, because up to 20 American athletes -- believed to include Olympic champions and world record holders -- tested positive for the substance at the U.S. national championships last summer.

The IAAF, which said Monday it was considering the legal implications, decided to proceed with the retesting following a meeting in Paris between IAAF president Lamine Diack and IAAF anti-doping chief Arne Ljungqvist.

"We're going to do it," IAAF spokesman Nick Davies said. "The legal issues aren't really that big. Our rules are quite clear: We have the right to do the tests. Now we just have to work out the details."

Any positive findings would lead to retroactive disqualifications, including stripping of any medals, and two-year bans.

"We want a clean sport," IAAF general secretary Istvan Gyulai told The Associated Press on Monday. "This is a great opportunity. We don't want to leave potential cheaters untouched."

Under the IAAF's drug-testing agreement with French authorities for the World Championships, all samples taken in France must be tested in France.

At the moment, however, only the UCLA doping control laboratory in Los Angeles has the ability to test for THG.

Davies said the IAAF would contact French officials and the UCLA lab. He suggested the samples could be sent to Los Angeles for analysis or the UCLA lab could provide the testing method to the French.

"We're under no time pressure," Davies said. "We'll do it the right way."

In potentially the biggest drug bust in sports history, the U.S. Anti-Doping Agency announced last Thursday that several athletes tested positive for THG at the U.S. track championships in June at Stanford, Calif.

USADA chief executive officer Terry Madden called it a widespread conspiracy involving chemists, athletes and coaches.

UCLA's lab developed a test for THG after an anonymous high-profile coach turned in a used syringe containing the substance. USADA retested 350 samples from the U.S. championships, as well as 100 samples from random out-of-competition tests.

The athletes who tested positive for THG haven't been identified pending analysis of their B samples. Some non-American athletes are also reportedly involved.

"The emergence of this new steroid is a matter of great concern and we are taking all steps that we can to investigate how widespread its use has been," IAAF president Lamine Diack said. "The IAAF is committed to the principle of re-testing all the Paris samples as part of this investigative process.

"If athletes have deliberately set out to cheat the public at our World Championships, then they must be exposed and dealt with in the strongest possible way."

The USADA believes the source of THG is a San Francisco area nutritional supplement maker called the Bay Area Laboratory Co-operative (BALCO), which was founded by current president Victor Conte.

BALCO's client list is said to include the world's fastest couple, Marion Jones and Tim Montgomery; San Francisco Giants superstar Barry Bonds; NFL player Bill Romanowski; and former tennis player Michael Chang.

Jones, who won a record five medals at the 2000 Games in Sydney; Montgomery, the world record holder in the 100; Bonds, the home run king who has vehemently denied using steroids; and New York Yankee slugger Jason Giambi, who used to play in the Bay area, are among 40 athletes to have been subpoenaed to appear before a federal grand jury in San Francisco, which this week will begin probing BALCO's finances.

American Kelli White, the double world sprint champion who faces losing her medals after testing positive for the stimulant modafinil in Paris, also has been called to appear before the grand jury.

"This is not the best thing to have an athlete's name connected with," said Ukranian coach Remi Korchemny, White's coach. "It is always going to affect you and it remains to be seen what his mind-set is."

Information from The Associated Press was used in this report.