By Jeremy Pelofsky

WASHINGTON (Reuters) - Prosecutors on Friday urged a federal judge to give them another chance at trying pitching star Roger Clemens for perjury after a mistrial was declared over their introduction of evidence that was banned.

Clemens, who is facing charges that he lied to Congress when he denied taking performance-enhancing drugs, asked Judge Reggie Walton to bar government prosecutors from getting another chance to try the case.

His lawyers argued another prosecution would violate his constitutional right against double jeopardy, which protects individuals from being tried twice on the same charges.

While admitting they made a mistake, the prosecutors insisted it was unintentional.

"As regrettable as this mistake was, it does not warrant the extreme measures of a prohibition on any retrial and the dismissal of defendant's indictment," prosecutors said in their 36-page motion opposing Clemens' request.

Clemens, 49, whose career spanned 24 years playing for four Major League Baseball teams and winning the Cy Young Award for best pitcher seven times, has been charged with lying to Congress in 2008 when he denied taking steroids and human growth hormones.

"The government's case was -- and is -- strong," the prosecutors said.

The mistrial was declared last month after prosecutors showed a video clip that appeared to bolster the credibility of a future witness, Clemens' former teammate Andy Pettitte, and referred to Pettitte's wife Laura, who said she had been told by her husband that Clemens used human growth hormones.

Pettitte was going to be a crucial witness during the trial because he recalled Clemens telling him that he used performance-enhancing drugs. Clemens says his old friend misremembered the conversation.

The judge had barred testimony by Pettitte's wife.

Prosecutors also said they had DNA evidence they planned to introduce linking Clemens to steroids found in the syringe and cotton balls kept by his former trainer, Brian McNamee.

Clemens' lawyers have described McNamee as a liar and said that he fabricated and manipulated the physical evidence.

The mistrial came just two days into presenting evidence, an embarrassing setback for prosecutors who were scolded by Walton for not being more careful. The judge said a lot of time and money had been wasted.

In their filing, the prosecutors formally apologized for the error.

"The government accepts responsibility for its oversight, and regrets the burdens that error has placed on this court and defendant," they wrote.

They said the judge's ruling about what could be used and what could not be used came days before jury selection and they had focused on the fact that Laura Pettitte could not be called as a witness, instead of whether references to her were embedded in other evidence.

The prosecutors also noted that the defense team had not objected immediately when the information was presented.

Walton has scheduled a hearing on the issue for September 2.

(additional reporting by James Vicini; Editing by Paul Simao)