Roger Clemens' attorney revealed Tuesday that the ex-baseball star plans to begin his defense against charges of lying to Congress by questioning whether lawmakers' investigation into whether he used performance-enhancing drugs was proper.

Clemens attorney Michael Attanasio said in court that the hearing the House Oversight and Government Reform Committee held in February 2008 had nothing to do with Congress' responsibility for legislation. He said the hearing was only concerned with airing a "credibility contest" between Clemens and his longtime trainer, Brian McNamee, who said he injected the pitcher with steroids and human growth hormone.

Clemens denied those allegations and has been charged with perjury, false statements and obstruction of Congress. The obstruction count charges Clemens with making 15 false or misleading statements to the committee, including his repeated denials he didn't take performance-enhancing drugs during his 24-season career and even whether he attended a 1998 pool party at Toronto Blue Jays teammate Jose Canseco's home in Miami.

McNamee says he saw Clemens and admitted steroids user Canseco off talking at the party with another man and that after they returned to Canada Clemens asked McNamee to inject him with steroids for the first time. Clemens and Canseco say Clemens was never at the party but was golfing at the time. Attanasio said that dispute suggests how improper the whole inquiry was and that jurors should be able to determine whether a "he said, he said debate" between Clemens and McNamee was a legitimate congressional concern.

"We're going to have a mini-trial on whether Roger Clemens went swimming," Attanasio said. "We're going to have a trial in U.S. District Court, Congress is going to have a hearing on these things? That's our point."

Assistant U.S. attorney Daniel Butler responded that the committee has responsibility for oversight that is broad and goes beyond legislation. He said steroids in baseball is a drug matter and pointed out that a 2005 hearing into the issue led to legislation to regulate steroids and triggered Major League Baseball to commission a report by former Sen. George Mitchell into the extent of the problem in the league.

The Mitchell report was released in December 2007 and named Clemens and 85 other current and former ballplayers as using drugs. Clemens denied the allegations and Butler pointed out that leaders of the House committee said they needed to investigate Clemens' denials to determine what weight to give the Mitchell report and its recommendations.

Attanasio argued that if the committee's purpose was to come full circle on the Mitchell Report, it had done so with a January 2008 hearing featuring testimony by Mitchell, baseball commissioner Bud Selig and former players union director Donald Fehr.

"That ship had left. That work was done. And now it becomes a question between Mr. Clemens and Mr. McNamee," Attanasio said.

But U.S. District Judge Reggie Walton said if "one of the icons of baseball" was taking exception to the Mitchell Report, "it seems to me that Congress has the authority to hold hearings to determine which view is correct."

Attanasio said the issue will be addressed in testimony from the first two witnesses prosecutors plan to call after opening arguments Wednesday morning. He said the first will be retired House Parliamentarian Charles Johnson, followed by Phil Barnett, who was chief counsel for the committee at the time it investigated Clemens.

The dispute over the committee's proper role came as Walton considered what preliminary instructions to give the jury, which he planned to seat Tuesday afternoon after three and a half days of screening potential members.