The newspaper said it had obtained a 15-page letter in which the agency said it had been in contact with "numerous riders, team personnel and others" who "will testify based on personal knowledge" of Armstrong's alleged doping.
The letter refers to data from blood samples obtained by the International Cycling Union in 2009 and 2010.
"This data is fully consistent with blood manipulation," including use of use erythropoietin, or EPO, a drug that controls red-blood-cell production, "and/or blood transfusions," the Journal reported the letter stated.
Armstrong, 40, who won the Tour de France from 1999 to 2005 while riding with the U.S. Postal Service team, has been banned from competition in triathlons, a sport he took up last year, until the charges are resolved, the Journal said.
"I have been notified that USADA, an organization largely funded by taxpayer dollars but governed only by self-written rules, intends to again dredge up discredited allegations dating back more than 16 years to prevent me from competing as a triathlete and try and strip me of the seven Tour De France victories I earned," the Journal reported Armstrong said in a statement.
The charges leveled by the USADA, which is based in Colorado Springs, Colo., aren't criminal in nature, but the agency has the power to ban athletes from competition and to revoke titles.