By Gene Cherry

RALEIGH, North Carolina (Reuters) - A decision on a contentious Olympic rule that could impact on dozens of athletes wanting to compete in the 2012 London Games is expected within the next four months, the Court of Arbitration for Sport (CAS) said on Wednesday.

IOC Rule 45, adopted in 2008, currently bars any athlete who receives a doping sanction of greater than six months from competing at the next Olympic Games.

The IOC has maintained the rule is not a sanction but an issue of eligibility and that it has the right to put conditions on participation in the Olympics.

But opponents of the rule, which include the U.S. Olympic Committee, say it violates the World Anti-Doping Agency (WADA) Code because it creates a second penalty for athletes who have already served their time.

The IOC and the U.S. Olympic Committee have asked CAS to determine the validity of the rule and the court said it would hold a hearing on August 17 with a verdict expected by the end of September.

Banned U.S. Olympic 400 meters champion LaShawn Merritt is among those who could have their eligibility for the London Games impacted by the CAS decision.

Merritt received a 21-month suspension after testing positive in 2009 and 2010 for a banned substance he said was found in a male enhancement product.

His ban ends in July but under the IOC rule he would be ineligible to compete in London.

But the U.S. panel of arbitrators who suspended the American said the rule could not be used to prevent him from competing in the 2012 U.S. Olympic trials or Olympic Games.

Current eligibility standards for the American team require an athlete to participate in the U.S. world championship trials. Merritt's ban, however, will not expire before the June trials.

No determination has been made on whether he would receive a waiver, U.S. officials have said.

(Editing by Julian Linden)