WASHINGTON — Roger Clemens and his accuser, Brian McNamee, will be the main witnesses at a House hearing on the Mitchell Report after Andy Pettitte and two others originally invited to testify were told tonight they don't need to show up.

Former Yankee Chuck Knoblauch and steroids dealer Kirk Radomski also were dropped from the witness list for Wednesday's public session. One new witness was added Monday night: a member of the staff that worked with former Senate majority leader George Mitchell to produce December's report on drugs in baseball.

But all attention will be focused on Clemens, a seven-time Cy Young Award winner, and McNamee, his former personal trainer, who alleged he injected the pitcher with performance-enhancing drugs.

"I guess it's showtime, isn't it?" Clemens' lead lawyer, Rusty Hardin, said in a telephone interview.

McNamee said in the Mitchell Report that he injected Clemens with steroids and human growth hormone at least 16 times in 1998, 2000 and 2001. Clemens' denials of those allegations drew the attention of the House Committee on Oversight and Government Reform.

Pettitte, a pitcher for the Yankees, gave a sworn deposition to committee lawyers last week, as did Clemens and McNamee. Knoblauch, a former major leaguer who was a Yankees teammate of Clemens and Pettitte, was interviewed by committee staff earlier, while Radomski had been scheduled for a pre-hearing meeting with the committee Tuesday.

All five originally were invited to testify Wednesday.

"Mr. Knoblauch and Mr. Pettitte answered all the Committee's questions and their testimony at the hearing is not needed," committee chairman Henry Waxman and ranking Republican Tom Davis said in a statement. "Mr. Clemens and Mr. McNamee have also cooperated with the Committee in its investigation."

Pettitte's request to be excused was first reported by The New York Times on its Web site.

Pettitte's attorney, Jay Reisinger, declined to comment after the announcement, while a lawyer for Radomski did not immediately return a phone message left at his office Monday night.

Asked about the change, Knoblauch's attorney, Diana Marshall, said: "I'm not disappointed. I know Chuck is not disappointed."