Not 30 minutes into his cross-examination of Roger Clemens’s chief accuser in the baseball legend’s perjury trial, defense attorney Rusty Hardin cut to the chase:

“Would you agree that whether or not Roger Clemens used steroids depends upon whether you are telling the truth?”

The witness, Brian McNamee, never got a chance to answer. A federal judge cut him off, agreeing with prosecutors that the question was better answered by jurors. But the query nevertheless highlighted the high stakes of what may turn out to be the trial’s key moment — the cross-examination of the only person with first-hand knowledge of Clemens’s alleged use of performance-enhancing drugs.

The importance of the testimony was also reflected in the august wood-paneled federal courtroom in the District, which on Wednesday had the air of a playoff game. The gallery was packed with spectators as well as a gaggle of reporters and relatives of the prosecutors, defense attorney and Clemens. A few attorneys, uninvolved in the matter, attended to catch what promised to be a dramatic show.

Hardin picked up right where he left off questioning McNamee briefly on Tuesday afternoon: aggressively trying to lay the ground work for his argument that Clemens’s former friend and strength coach cannot be trusted.

A flamboyant attorney clad in a cream-colored seersucker suit and an orange tie as bright as a reflective safety vest, Hardin spoke in a quick Southern drawl and jabbed his left finger at McNamee while pressing him about his motives and inconsistent statements. At one point, Hardin dramatically placed an easel next to the witness. In large black letters, Hardin wrote, “Mistake,” “Bad Memory” and “Lie” — categories, he said, that would help to classify the witness’s past statements.

Despite the pressure, the former New York City police officer mostly held his ground over two hours of questioning. At one point, he even challenged the defense lawyer by saying, “You have to ask Roger that.”

McNamee, 45, is expected to return to the witness stand on Thursday for more questioning, which is only expected to grow more heated as Hardin delves into the trainer’s checkered past.

The trial started last month and is the second crack federal prosecutors are getting at “The Rocket” on charges he lied to Congress in 2008 when he denied ever having taken performance-enhancing drugs. The first trial was halted last year when prosecutors presented prohibited evidence to jurors. This time around there has been more drama: another witness and former Clemens teammate, Andy Pettitte, agreed with defense attorneys that his memory of a key conversation was “fifty-fifty” at best.

Observers expected more fireworks Wednesday when Hardin got his first real opportunity to question McNamee. The strength coach, who worked with Clemens from 1998 through 2007, testified that he first heard the star pitcher mention steroids during spring training in 1998.

At the time, Clemens had already won three Cy Young awards and was in his second-year as a starting pitcher for the Toronto Blue Jays. McNamee was the team’s new strength coach. As pitchers were exercising in the outfield, McNamee testified he overheard Clemens mention that he didn’t play football at the University of Texas because he “wasn’t willing to take a shot in the thigh.”

A few months later, McNamee said, he overheard a conversation between Clemens and Jose Canseco, another Blue Jay, in which they discussed performance-enhancing drugs. McNamee testified he could not recall specifics of the conversation but Clemens later approached him and asked if the strength coach could “help me with the booty shot. I can’t do the booty shot.”

Not long after that conversation, McNamee was summoned to Clemens’s apartment where he found steroids, alcohol and a needle laid out in the bathroom, McNamee testified.

He said he gave Clemens a shot of the substance in the pitcher’s buttocks. Over the next few months, he injected Clemens more than a dozen times. He resumed the injections in 2000 and 2001, when Clemens was pitching for the New York Yankees and McNamee was the club’s assistant strength coach.

Though McNamee testified in great detail about the injections last week, Hardin highlighted inconsistencies in his statements over the years.

“Would you agree with me that over the last four years your testimony and your memory and statements have sort of evolved about what happened?” Hardin asked.

“It’s fair to say my recollections of certain things have gotten better,” McNamee replied, refusing to yield any ground.

McNamee then recalled another conversation with Clemens about steroids — in early 2004 — that he had never relayed to federal investigators or those working for former senator George Mitchell, who issued a lengthy report in 2007 that exposed rampant steroid use in Major League Baseball. McNamee said that Clemens told him: “I want to get really huge. Do you still have that guy?” Clemens was referring to his strength coach’s former steroid supplier, McNamee said.

McNamee has testified that he regretted injecting Clemens because it was the wrong thing to do. Since it became public that he cooperated with federal investigators and Mitchell, McNamee said he has struggled to hold down paying jobs.

Hardin, however, painted McNamee as a man seeking to benefit financially from the star’s downfall. “Wouldn’t you agree that ever since February 2008, you have been seeking to take advantage of the fame you achieved by making allegations against Roger Clemens?” Hardin asked.

“Can you repeat that, please?” McNamee asked.

“No, I’ll move on,” said Hardin, who then quizzed the witness about a self-published memoir, a Web site business that never took off and his disposition of memorabilia signed by Clemens.

Though he often paused for several seconds before answering questions and seemed confused at times, McNamee did not hesitate to counter-punch.

When Hardin asked McNamee how many shots a ballplayer like Clemens could expect to receive over the course of his career, McNamee responded: “Including the ones I gave him?”