WASHINGTON — Roger Clemens and Andy Pettitte were asked today to testify before a congressional committee on January 16, along with their former trainer, Brian McNamee.

Also invited to appear before the House Oversight Committee were a former Mets clubhouse attendant, Kirk Radomski, whose allegations were a central part of last month’s Mitchell report on doping in baseball. A former All-Star second baseman, Chuck Knoblauch, also was asked to speak to the panel.

“It could be a circus with players, true,” the committee’s minority staff director, David Marin, said in a telephone interview. “But if you tailor it right and invite people who clearly have pertinent information about the substance of the report, then it’s anything but a circus. It’s substantive. That’s what Democrats and Republicans have agreed to here.”

A day earlier, the committee is to hear testimony from the baseball commissioner, Bud Selig, a union leader, Donald Fehr, and a former Senate majority leader, George Mitchell.

“The original hearing was called to examine the Mitchell recommendations and findings. The committee has decided to hold a second day of hearings for the very same reason — to invite people with varying perspectives on the Mitchell report to shed further light on it,” Mr. Marin said.

Mr. McNamee told Mr. Mitchell he had injected Mr. Clemens, a seven-time Cy Young Award winner, with steroids and human growth hormone during the 1998, 2000 and 2001 seasons. Mr. Clemens, in an interview to be broadcast by CBS’s “60 Minutes” on Sunday, said Mr. McNamee injected him with vitamins and painkillers but not performance-enhancing drugs.

Mr. Pettitte acknowledged Mr. McNamee injected him with HGH twice while the pitcher was recovering from an injury.

Mr. McNamee told Mr. Mitchell he acquired HGH from Radomski for Mr. Knoblauch in 2001, and that he injected him with it.

Radomski pleaded guilty in April to federal felony charges of distributing steroids and laundering money, and he is scheduled to be sentenced February 8.

Although none of the people asked to testify under oath January 16 had agreed to appear as of late this afternoon, the committee’s announcement listed Mr. Clemens and others under the heading, “Witnesses will include.”

“We always presume that invited witnesses will appear,” Mr. Marin said.

E-mails to attorneys for Messrs. Clemens and McNamee and a phone call to Radomski’s lawyer were not immediately returned.

This is the same panel of lawmakers that convened the March 2005 hearing where Mark McGwire refused to say whether he had used performance-enhancing drugs. Sammy Sosa said he had never knowingly used illegal performance-enhancing drugs, while Rafael Palmeiro denied using drugs but tested positive later that year for a steroid.

The leaders of the committee, Reps. Henry Waxman and Tom Davis, were among several members of the House and Senate who sponsored legislation in 2005, proposing to mandate stronger steroid testing and penalties for baseball and other American professional sports leagues.

Another committee has scheduled a January 23 hearing on the Mitchell report.