By Lily Kuo

WASHINGTON (Reuters) - Former baseball pitching ace Roger Clemens arrived in court on Monday for a new trial on charges he lied to Congress about taking steroids, nine months after a judge stopped his first trial in its opening days because of a misstep by prosecutors.

The seven-time Cy Young Award winner sat tapping a pen on his knee and occasionally taking notes as lawyers began selecting from a pool of 90 potential jurors in his perjury and obstruction case in District Court. The presiding judge said he expected the trial to last up to six weeks.

When introduced, Clemens stood, faced the potential jurors and said, "Good morning, good morning."

Clemens was indicted in 2010 over testimony to Congress in 2008 in which he denied taking steroids and human growth hormones. Prosecutors say they have evidence to the contrary and will seek to discredit Clemens in what promises to be a high-profile trial.

Prosecutors on Monday read out the names of more than 60 potential witnesses, while defense lawyers ticked off a list of about 30 names. The included current and former New York Yankees Andy Pettitte, Paul O'Neill and Mike Stanton, who all played with Clemens.

U.S. District Court Judge Reggie Walton declared a mistrial after two days of arguments during Clemens' first trial in July 2011. Prosecutors showed jurors a video clip that included material the judge had banned from the case unless the information was raised by Clemens' defense team.

Walton agreed to a new trial after prosecutors said the error in the first attempt was not intentional.

The allegations that Clemens, 49, used performance-enhancing drugs has raised questions about his record. Known as "The Rocket," Clemens played for four teams over a 24-year career and his seven Cy Young wins for best pitcher in his league are a record.

Clemens is one of the biggest names linked to steroid use in baseball. Other stars who have faced questions about doping include sluggers Mark McGwire and Jason Giambi and home-run king Barry Bonds.

Doping, or using performance-enhancing substances in professional sports, is not in itself a federal crime - but the government has chosen, with mixed results, to pursue cases against athletes who it believes have either committed fraud or lied when called to testify about using performance-enhancing drugs.

In one setback, federal prosecutors in February dropped a two-year investigation centered on whether seven-time Tour De France champion Lance Armstrong and his teammates cheated the sponsor of their bike racing team with a secret doping program. Armstrong has always denied using performance-enhancing drugs.

Clemens' lawyers this month objected to prosecutors' bid to ban some of the arguments he used in last year's trial. They said prosecutors did not object when those arguments were used in an opening statement.

U.S. prosecutors had sought last month to bar defense statements, including suggestions that the government resources used in the case against Clemens were "excessive or wasteful."

During the first trial, Clemens' defense team referred to more than 100 investigators used in the probe and suggested that the government had spent millions of dollars on the case.

They also asked that any reference to the botched first trial be excluded from the second.

In the first trial, prosecutors promised several witnesses to prove Clemens took the performance-enhancing drugs and then lied about it, including Pettitte and his former trainer Brian McNamee.

Defense attorneys have branded McNamee a liar and, according to media reports, said at a hearing on Friday they may challenge key physical evidence handed over to prosecutors by the trainer.

(Reporting By Ian Simpson and Lily Kuo; Editing by Jackie Frank)