VISALIA, Calif. — After four years of maintaining his innocence about doping charges that ruined his reputation and caused him to be stripped of his 2006 Tour de France title, the American cyclist Floyd Landis has sent e-mail messages to several cycling officials in the United States and in Europe in which he admits using performance-enhancing drugs for most of his career.

Two of those officials said that Landis’s messages provided a detailed description of doping that began in 2002, Landis’s first year alongside Lance Armstrong. Both were riding for the successful but now-defunct United States Postal Service team. The two officials who received the e-mail messages did not want their names published, citing continuing investigations, including by federal authorities, into the content of the messages.

In the messages, which were first reported by The Wall Street Journal, Landis accused other top American cyclists on the Postal Service team, including Armstrong, of using performance-enhancing drugs and methods. Other cyclists named were George Hincapie, the current United States road racing national champion; Levi Leipheimer, the three-time Tour of California champion; and David Zabriskie, the five-time United States time trial champion.

“I would say I’m surprised, but I’m not,” Armstrong said Thursday morning before competing in Stage 5 of the Tour of California. Armstrong said that Landis had been sending him e-mail and text messages for the past couple of years suggesting that he would go public with accusations about him and that the messages reached “a fever pitch” last month.