The agency did not say that Armstrong ever failed a test, but his former teammates testified as to how they beat tests or avoided the tests altogether.
The New York Times, citing unnamed associates and anti-doping officials, said Armstrong has been in discussions with USADA officials and hopes to meet with David Howman, chief of the World Anti-Doping Agency. The newspaper said none of the people with knowledge of Armstrong's situation wanted to be identified because it would jeopardize their access to information on the matter.
Armstrong: The legend and the fall
Armstrong has been an icon for his cycling feats and celebrity, bringing more status to a sport wildly popular in some nations but lacking big-name recognition, big money and mass appeal in the United States.
He fought back from testicular cancer to win the Tour from 1999 to 2005. He raised millions via his Lance Armstrong Foundation to help cancer victims and survivors, an effort illustrated by trendy yellow "LiveSTRONG" wristbands that helped bring in the money.
But Armstrong has long been dogged by doping allegations, with compatriot Floyd Landis -- who was stripped of his 2006 Tour de France title after failing a drug test -- making a series of claims in 2011.
Armstrong sued the USADA last year to stop its investigation of him, arguing it did not have the right to prosecute him. But after a federal judge dismissed the case, Armstrong said he would no longer participate in the investigation.
In October 2012, Armstrong was stripped of his titles and banned from cycling. Weeks later, he stepped down from the board of his foundation, Livestrong.