The letters ask the witnesses to meet with committee staff on specific dates leading up to the panel's scheduled Feb. 13 hearing.
"The committee asks that you provide testimony about allegations in Senator George Mitchell's report ... that you and other Major League Baseball players used performance enhancing drugs during your professional baseball career," Waxman and Davis wrote to Clemens.
The letter was sent to him via Rusty Hardin, one of the lawyers for the seven-time Cy Young Award winner. Clemens was given until Tuesday to respond.
"We look forward to sitting down with the committee staff on the 26th and with the full committee at its public hearing on February 13th," Hardin said.
The Mitchell Report, released last month, contains McNamee's allegations - first told to federal prosecutors, then repeated to the former Senate majority leader - that he injected Clemens with steroids and human growth hormone.
Clemens has repeatedly and vigorously denied what McNamee said, including in a recorded television interview and a live news conference.
McNamee, whose lawyer said Thursday he was told his request for immunity for congressional testimony was likely to be rejected, was asked to meet with committee staff Jan. 31.
"The committee asks that you provide testimony about the information you supplied to Senator Mitchell regarding the use of performance enhancing drugs by Major League players," the letter to McNamee reads.
Clemens' former teammate and workout partner, Andy Pettitte, was asked to appear Jan. 30, while another former teammate, Chuck Knoblauch, was invited for Jan. 24. Pettitte has acknowledged that McNamee injected him with HGH. Kirk Radomski, a former New York Mets clubhouse employee who along with McNamee was one of the Mitchell Report's key sources, was asked to speak to staff Feb. 1.
"I don't think there's any great tea leaves to be read in that sequence," said Richard Emery, one of McNamee's lawyers. "I don't think there's any great significance to the order."
The witnesses were given the choice of a deposition or a transcribed interview.
"I haven't detected any preference" for one format or the other, said Keith Ausbrook, Republican general counsel for the committee. "At this point, we're still in discussions."
Among the differences is that a deposition is delivered under oath and an interview is not, although that isn't a major distinction, because it is a crime to lie to Congress. Waxman and Davis this week asked the Justice Department to investigate whether 2002 AL MVP Miguel Tejada made false statements to House committee staff when he was interviewed - not under oath - in connection with the Rafael Palmeiro perjury case in 2005. The FBI has opened a preliminary investigation.
"If you're not under oath, you might as well be, because you're subject to prosecution," Emery said.
With a deposition, the transcript is kept confidential until the committee chairman and ranking minority member agree to release it or if the committee votes to release it. With a transcribed interview, the committee may talk about its contents and release it at any time.
In addition, with a deposition, only one Democrat and one Republican may ask questions of the witness, whereas more members of committee staff are allowed to participate in an interview.
A witness may be accompanied only by an attorney at a deposition; a witness may request that others be present at an interview.
