BERLIN, April 3- German-based anti-graft watchdog Transparency International on Monday called on sport governing bodies to tackle corruption with coordinated efforts in a warning just two months before soccer's World Cup.

The German chapter of the Berlin-based agency said risks of corruption in sport, especially soccer, had become an increasing problem in the wake of growing commercial influences.

It warned recent betting scandals showed the vulnerability of sport to criminal manipulation and said it planned to set up a working group to study antidotes. The agency also warned sport officials against complacency.

"The increasing importance and commercialism of sport raise the danger of results being manipulated," said Hansjoerg Elshorst, chairman of Transparency International-Germany (TI-D), at a news conference ahead of the June 9-July 9 World Cup.

"Despite the number of individual cases recently there has been far too little public discussion of corruption in sport," Elshorst said, referring to a series of betting scandals and accusations that have plagued German soccer in the last year.

The agency, which views doping as well as match fixing as threats to the image of sport, hopes to promote co-operation among federations to improve the overall transparency.

It also called for aggressive investigation into suspicions of fraud and measures to improve corruption prevention.

Officials said they could not quantify how widespread -- or limited -- corruption is now but in the wake of the high-profile soccer betting scandals in Germany and doping at the Olympics they expressed fears corruption could tarnish all sport.

German soccer leaders had expressed hope a scandal around disgraced referee named Robert Hoyzer, convicted of fraud and banned for life for his bid to rig nine matches in a two million euro ($2.4 million) betting fraud in 2004, was an aberration.

But there have been new reports of alleged corruption in the last month -- one state prosecutor investigation involves a Bundesliga team, Bayer Leverkusen, that battled to avoid relegation in 2003 and another around suspected attempts by a betting ring to influence results of regional league matches.

"Sport lives from its positive image and that's why it's especially susceptible to corruption," said Silvia Schenck, a member of a working committee and former German cycling federation president.