BEIJING — China's top backstroker Ouyang Kunpeng has been banned for life for failing a doping test, a major embarrassment for the host country just six weeks before the Beijing Olympics.

In a statement Friday, the Chinese Swimming Association said Ouyang tested positive for a doping substance on May 1. It gave no details about the substance. The CSA said Ouyang's coach Feng Shangbao was also given a life ban.

Ouyang was not considered a contender for gold at the Olympics. China is expected to produce few winners in the pool and has won only one gold medal in swimming in the past two Olympics. The top candidate is probably Wu Peng in 200 meter butterfly.

Ouyang won three silver medals at the 2006 Asian Games.

China is hoping to overshadow problems leading up to the games — including choking air pollution, chaotic protests on the torch relay and issues of freedom of the press — by topping the gold-medal table and overtaking the United States.

Any positive doping test by a Chinese athlete during the Olympics would be a major blow.

"The Chinese Swimming Association has made lots of effort on anti-doping, however this positive test case still happened," the statement said. "It's a big lesson, and we need to stay alert on anti-doping and pay constant attention."

"The Chinese Swimming Association strongly opposes doping and is cracking down on doping to guarantee a fair-play environment, to protect athletes' health and guarantee athletes are clean when competing in Olympics."

Chinese swimmers were involved in a series of doping scandals in the 1990s. In the past year, under pressure from the World Anti-Doping Agency, China has begun toughening its drug testing and is also trying to close factories in China that produce performance-enhancing drugs and sell over Web sites.

The China Anti-Doping Agency recently opened a new laboratory that will do 4,500 doping tests for the Olympics. This is up 25 percent from Athens.