Lance Armstrong is gearing up to admit that he was doping throughout his illustrious cycling career ... and he will make the admission to Oprah Winfrey this week ... so says a new report.

Armstrong will not go into great detail, says USA Today, but will make the admission during an interview that tapes Monday and airs on Thursday.

The seven-time Tour de France winner has adamantly denied any wrongdoing for years, often attacking anyone who accused him.

Armstrong was banned for life and stripped of all his Tour de France victories last year.