By Gene Cherry RALEIGH, North Carolina (Reuters) - Olympic champion Justin Gatlin was banned for up to eight years after agreeing that his positive drug test constituted a doping violation, the U.S. Anti-Doping Agency (USADA) said on Tuesday.

The actual length of the ban, which came into effect on August15, will be determined by an arbitration panel. Gatlin, who has agreed to co-operate with USADA to eradicate drugs in sport, will lose the world 100 metres record of 9.77 seconds he shares with Jamaican Asafa Powell unless the ban is overturned at the arbitration hearing, USADA said.

Gatlin tested positive for the male sex hormone testosterone at the Kansas Relays in April for reasons he said he did not know. It was his second positive test, which under anti-doping rules could have resulted in a life ban.

Gatlin's attorney John Collins said the 24-year-old sprinter would seek through arbitration a suspension far less than eight years.

"We believe this is an exceptional circumstances case," Collins said via telephone from Chicago. "The last time I represented Justin, the (arbitration) panel specifically found that he neither cheated nor intended to cheat, and I expect when all facts and circumstances in this case come out, there will be a similar finding, " Collins said.

Gatlin tested positive in 2001 for an amphetamine contained in a medication he had been taking for 10 years for Attention Deficit Disorder. He was suspended for two years.

The International Association of Athletics Federations (IAAF) later found Gatlin had not intentionally committed a doping violation and reinstated him after one year. The IAAF warned Gatlin that he would face a life ban if he was charged with another doping offence.

UNIQUE CATEGORY

USADA said on Tuesday, however, that the circumstances of Gatlin's first offence put the violation in a unique category.

"Given these circumstances and consistent with the international CAS precedent, a maximum of an eight-year suspension is a fair and just outcome," USADA chief executive officer Terry Madden said in a statement.

If the ban is not overturned, Gatlin's ineligibility would run through July 24, 2014, USADA said. He would also forfeit results from April 22, the date of the positive test. Gatlin agreed to the accuracy of the laboratory results from his April drugs test, USADA said.

Both U.S. Olympic Committee (USOC) chairman Peter Ueberroth and USADA general counsel Travis Tygart applauded Gatlin.

"Justin Gatlin is doing the right thing by stepping forward and acknowledging that he committed a doping offense," Ueberroth said in a statement. "Since becoming an elite-level athlete, Justin has talked about the importance of eradicating doping in sport."

"By acknowledging his doping positive and agreeing to work with USADA, Justin now has an opportunity to put those words into action," Ueberroth said. "He can play a meaningful role in solving a problem that is reaching a crisis level in American sport."

Tygart said; "Instead of wasting everyone's time and resources with frivolous technical arguments, they (Gatlin and his team) have accepted the consequences and want to move forward."

SECOND AMERICAN

Gatlin becomes the second American to lose the 100 metres world record because of a doping offence. Tim Montgomery was banned from the sport for two years in 2005 based on evidence from the BALCO doping scandal, and his 2002 record time of 9.78 seconds was expunged.

"That should provide a substantial notice to all athletes out there that no one is above the rules," Tygart said.

Gatlin becomes at least the seventh athlete trained by coach Trevor Graham to be charged with a doping offence. Graham has denied providing illicit substances to athletes, but is under investigation by the IAAF and USADA, according to the IAAF.

Tygart would not comment on that investigation, saying USADA's investigation into the BALCO doping scandal was continuing.

USA Track & Field chief executive officer Craig Masback said Gatlin's case was a setback for the sport. "While we are glad Justin has taken responsibility for his positive test and will co-operate in USADA's anti-doping efforts, we are sorely disappointed in him," Masback said.