LOS ANGELES - Federal prosecutors on Friday dropped an investigation centered on whether seven-time Tour De France champion Lance Armstrong and his teammates cheated the sponsor of their bike racing team with a secret doping program.The decision means that Armstrong, a cancer survivor who has always vehemently denied using performance-enhacing drugs, will not face any charges following the two-year-long probe.Prosecutors have said little publicly about the case and U.S. Attorney Andre Birotte Jr., in a brief written statement, announced simply that his office was "closing an investigation into members and associates of a bicycle racing team owned in part by Lance Armstrong.”A source familiar with the investigation, however, told Reuters that prosecutors had been looking into whether the team had defrauded its sponsor, the U.S. Postal Service, by doping.Doping, or using performance enhancing substances in professional sports, is not a federal crime."I am gratified to learn that the U.S. Attorney’s Office is closing its investigation. It is the right decision and I commend them for reaching it,” Armstrong, 40, said in a statement released through his spokesman.Birotte said that he was making a public announcement that the investigation had been closed because of "numerous reports about the investigation in media outlets around the world.”