WASHINGTON — Roger Clemens’s denial of steroid use warrants further investigation, Congress said today in asking the Justice Department to determine whether the star pitcher lied under oath in testimony to a House committee.

The chairman of the House Oversight and Government Reform Committee, Henry Waxman, and the ranking Republican, Tom Davis, sent a letter to Attorney General Mukasey, urging more scrutiny of Mr. Clemens’s statements in a February 5 sworn deposition and at a February 13 public hearing where he said he “never used anabolic steroids or human growth hormone.”

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“That testimony is directly contradicted by the sworn testimony of Brian McNamee, who testified that he personally injected Mr. Clemens with anabolic steroids and human growth hormone,” the congressmen wrote.

“Mr. Clemens’s testimony is also contradicted by the sworn deposition testimony and affidavit submitted to the committee by Andrew Pettitte, a former teammate of Mr. Clemens, whose testimony and affidavit reported that Mr. Clemens had admitted to him in 1999 or 2000 that he had taken human growth hormone,” the letter said.

Mr. Clemens declined to comment today when approached by reporters at the Houston Astros’ spring training camp in Kissimmee, Fla. Mr. Pettitte, with the New York Yankees in Florida, declined comment through a team spokesman.

“Now we are done with the circus of public opinion, and we are moving to the courtroom,” Mr. Clemens’s lead lawyer, Rusty Hardin, said. “Thankfully, we are now about to enter an arena where there are rules and people can be held properly accountable for outrageous statements.”

Mr. McNamee, Mr. Clemens’s former personal trainer, told federal prosecutors, a baseball investigator, George Mitchell, and Congress that he injected the seven-time Cy Young Award winner at least 16 times with human growth hormone and steroids from 1998 to 2001. Mr. Clemens repeatedly and vigorously denied the allegations.

Congress turned its attention to the matter because Mr. Clemens’s denials questioned the legitimacy of the Mitchell Report, prepared by the former Senate majority leader and released in December.

After both men stuck to their stories under oath, first separately in closed-door depositions and then while sitting a few feet from each other at this month’s hearing, it was expected that one or the other — or perhaps both — would be referred to the Justice Department for a criminal inquiry.

Instead, only Mr. Clemens faces a possible perjury investigation, after the committee decided not to refer Mr. McNamee.

Mr. Waxman sent committee Democrats an 18-page memo prepared by his staff outlining reasons for the criminal referral. The memo summarizes “seven sets of assertions made by Mr. Clemens in his testimony that appear to be contradicted by other evidence before the committee or implausible.”

Those areas involve Clemens’s testimony that he has “never taken steroids or HGH,” that Mr. McNamee injected him with the painkiller lidocaine, that team trainers gave him pain injections, that he received many vitamin B-12 injections, that he never discussed HGH with Mr. McNamee, that he was not at the house of a then-teammate, Jose Canseco, between June 8 and 10, 1998, and that he was “never told” about Mr. Mitchell’s request to speak.

Mr. Davis, who was the chairman of the committee when it held its 2005 hearing with Mark McGwire and Rafael Palmeiro, said the referral focuses on the core question of whether Mr. Clemens used performance-enhancing drugs.

“Some may want to ‘help’ the Department of Justice by characterizing evidence or packaging apparently contradictory quotes on other questions to help make a case for perjury. I don’t think that’s necessary,” Mr. Davis said. “The record speaks for itself, and it tells me the question of Mr. Clemens’ truthfulness demands further analysis by law enforcement.”

Neither Mr. Waxman nor Mr. Davis responded to interview requests.