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Lawyers for former Major League Baseball pitching great Roger Clemens branded the prosecution's main witness a liar as they presented closing arguments to the jury on Tuesday in a perjury trial that has lasted more than two months.

The defense launched a final assault on the credibility of Brian McNamee, Clemens' former trainer and the most important prosecution witness who has testified he injected Clemens with anabolic steroids and human growth hormone between 1998 and 2001.

"Saying Brian McNamee lies zero times is sort of like calling the Grand Canyon a ditch," Clemens' lawyer Rusty Hardin told the jurors as they prepared to begin deliberations after hearing from 46 witnesses in the closely watched trial.

Prosecutors made the first part of their closing arguments earlier in the day. They told jurors that Clemens - one of the greatest pitchers in baseball history - had weaved an "entangled web of lies" to protect his reputation. Clemens did not testify in the trial.

"What is this case about?" Assistant U.S. Attorney Gilberto Guerrero asked. "This case is not about Roger Clemens' greatness. It is about (him) lying ... to protect his legacy."

"We're not asking you to like Brian McNamee. ... Brian McNamee did a lot of things that weren't nice ... but Roger Clemens is the one who chose Brian McNamee to inject him with steroids and HGH," Guerrero told the jury.

Clemens, 49, is on trial for the second time on federal charges of lying in 2008 to the House of Representatives' Committee on Oversight and Government Reform, which was investigating drug use in baseball. Clemens' first trial ended in a mistrial.

He is among the biggest baseball stars accused of using performance-enhancing drugs.

Clemens faces one count of obstruction of Congress, three counts of making a false statement and two counts of perjury.

Prosecutors were due to finish their closing arguments in the afternoon and the jury was expected to begin deliberating later Tuesday or Wednesday morning.

Clemens' lawyers on Tuesday continued their strategy of portraying McNamee as unreliable and a liar.

McNamee was the prosecution's only witness with first-hand knowledge of Clemens' alleged drug use.

'TALE OF TWO MEN'

In remarks that veered from impassioned appeal to attempts at comic relief, Hardin described the trial as a "tale of two men." He showed jurors a pair of photos, one of Clemens smiling in a baseball cap and another of a pallid and squinting McNamee.

With a chart of statements by McNamee organized into categories for mistakes, admitted lies, and proven lies, defense lawyers offered reasons why McNamee's testimony could not be believed "beyond a reasonable doubt," the standard jurors must apply when judging whether or not Clemens is guilty.

Clemens' lawyers said McNamee contradicted himself throughout the investigation and trial and had not just lied about his motives for keeping medical waste he later turned in to authorities, but "made up this story" about doing so to keep his wife off his back.

McNamee had testified that he kept needles, cotton balls, a broken steroid ampoule and other medical waste from injections for Clemens to comfort his now estranged wife who said he would "go down" for his involvement in drug usage in baseball.

McNamee's wife, Eileen, later testified that she had never made such a warning to McNamee.

"Brian McNamee defines reasonable doubt, standing up there on his own," Clemens attorney Michael Attanasio said.

The defense has worked to portray Clemens as a hard worker whose late-career success was the product of dedication and smart pitching, not performance-enhancing drugs.

Clemens won 354 regular-season games and is a record seven-time winner of the yearly Cy Young Award as best pitcher. Clemens won his final Cy Young Award in 2004, the summer he turned 42, in his first season with the Houston Astros.

(Editing by Will Dunham)