By Alan Baldwin

RIO DE JANEIRO (Reuters) - Michael Phelps, the most medaled Olympian of all time, questioned on Wednesday whether he had ever swum in a 'clean' sport as he prepared for a Rio Games overshadowed by the Russian doping scandal.

"We all want clean sports," the American told a news conference. "We want everybody to be on the same playing field.

"I think I can honestly say as well in my career I don't know if I've ever competed in a clean sport," added the 31-year-old, winner of 18 career Olympic golds and 22 medals. "And it's upsetting."

Phelps, who will carry the flag for the United States at Friday's opening ceremony, said there was not much he could control other than his own actions and that would be his priority.

However, his long-standing coach Bob Bowman was scathing about the situation.

"Clearly from a team perspective we are just focused on getting the best performances that we can, regardless of the circumstances," he said, sitting alongside Phelps.

"But I would have to say from a personal standpoint, it's very concerning to me that our governing bodies have dropped the ball in many ways on this. The system is broken and it has to be fixed."

Dozens of Russian athletes have been banned from the Olympics, including essentially the entire track-and-field team, after revelations through whistleblowers of a systematic, state-backed doping program in the country.

But the International Olympic Committee (IOC) has come under fire for not imposing a blanket ban.

Seven Russian swimmers -- Yulia Efimova, Mikhail Dovgalyuk, Natalia Lovtcova, Anastasia Krapivina, Nikita Lobintsev, Vladimir Morozov and Daria Ustinova -- have been banned by the governing body FINA from competing at Rio.

However, the status of Lobintsev and Morozov remains uncertain after they appealed to the Court of Arbitration for Sport (CAS).

Asked what he would do to clean up the sport if he were running FINA, Phelps ducked the question but said he agreed with Bowman about the state of sport as a whole.

"I think there's something that needs to change about all sports, not just swimming," he said. "As athletes you want to be able to compete on an even playing field.

"We've had this problem for how many Olympics now? It seems almost every time there's something that comes up. And it's sad. It's really sad that we can't control it - that somebody who is in charge cannot control it."

(Editing by Rex Gowar)