In a testy exchange of letters and statements revealing the gulf between the two sides, USADA urged Armstrong to testify under oath to help "clean up cycling."
Armstrong's attorneys responded that the cyclist would rather take his information where it could do more good—namely to cycling's governing body and World Anti-Doping Agency officials.
USADA's response to that: "The time for excuses is over."
The letters, obtained Friday by The Associated Press, underscore the continuing feud between Armstrong and USADA CEO Travis Tygart, the man who spearheaded the investigation that uncovered a complex doping scheme on Armstrong's U.S. Postal Service teams.
Armstrong's seven Tour de France victories were taken away last year and he was banned for life from the sport.
In an interview with Oprah Winfrey last week, Armstrong admitted doping, said he owed a long list of apologies and that he would like to see his lifetime ban reduced so he can compete again.
His most realistic avenue toward that might be telling USADA everything he knows in a series of interviews the agency wants started no later than Feb. 6.
That seems unlikely.
Armstrong attorney Tim Herman responded to USADA's first letter, sent Wednesday, by saying his client's schedule is already full, and besides, "in order to achieve the goal of 'cleaning up cycling,' it must be WADA and the (International Cycling Union) who have overall authority to do so."
By Friday night, Herman strongly suggested Armstrong won't meet with USADA at all but intends to appear before the UCI's planned "truth and reconciliation" commission.
"Why would we cooperate (with USADA)?" Herman said in a telephone interview. "USADA isn't interested in cleaning up cycling. Lance has said, 'I'll be the first guy in the chair when cycling is on trial, truthfully, under oath, in every gory detail.' I think he's going testify where it could actually do some good: With the body that's charged with cleaning up cycling," Herman said.
In its last letter to Armstrong, sent Friday evening, USADA attorney William Bock said his agency and WADA work hand-in-hand in that effort.
"Regardless, and with or without Mr. Armstrong's help, we will move forward with our investigation for the good of clean athletes and the future of sport," Bock's letter reads.
The letters confirm a Dec. 14 meeting in Denver involving Armstrong, Tygart and their respective attorneys, which is when, in Tygart's words, Armstrong should have started thinking about a possible meeting with USADA.
"He has been given a deadline of February 6th to determine whether he plans to come in and be part of the solution," Tygart said in a statement. "Either way, USADA is moving forward with our investigation on behalf of clean athletes."
The letters were sent to the AP after details about a Tygart interview with "60 Minutes," being aired Sunday, were made public.
Among Tygart's claims: Armstrong is lying when he says he didn't dope during his 2009-10 comeback.
Tygart said USADA's report on Armstrong's doping included evidence Armstrong was still cheating in those years.
"His comeback was totally clean," Herman said. "It's pretty fashionable to kick Lance Armstrong around right now."
Tygart also reiterated that an Armstrong associate offered USADA a donation of more than $200,000. Armstrong denied that in his interview with Winfrey, too.
In advancing his claim that USADA is only a bit player in the investigation, Herman noted in his letter, sent to USADA on Friday, that most cycling teams are based in Europe.
"I'm pretty sick of people trying to blame a European cycling culture that goes back to the 1920s on one guy," Herman said.
Bock's response to that: "Your suggestion that there is some other body with which Lance should coordinate is misguided," he said in his final letter.
AP National Writer Eddie Pells contributed to this report.