WASHINGTON – Prosecutors in the Roger Clemens perjury case said Friday they had made an honest mistake in showing jurors inadmissible evidence, and that shouldn’t save the baseball star from facing a new trial.

The prosecutors filed arguments disputing Clemens’ position that a second trial would violate his constitutional protection against double jeopardy by making him face the same charges twice.

Clemens had argued the showing of the evidence was a deliberate ploy to invoke a mistrial because the prosecutors’ case was going badly. But the prosecutors say their case remains strong and Clemens wants to “gain an unwarranted windfall from this inadvertent error.”

The prosecutors said it was an oversight when they showed jurors a video clip that mentioned that Clemens’ teammate told his wife that Clemens admitted using performance-enhancing drugs — evidence the judge had ruled inadmissible. The filing is the prosecutors’ first public admission of wrongdoing in the case and first explanation of what went wrong.

The prosecutors wrote it was their duty to make sure evidence was not included in their exhibits. “The government accepts responsibility for its oversight, and regrets the burdens that error has placed on this court and defendant,” they wrote, but argued the mistake was because of the press of other trial matters and was not intentional.

That’s an important point for the prosecutors to make to the judge, who has scheduled a Sept. 2 hearing on the retrial debate. Normally, when a defendant requests a mistrial, a second trial is not considered double jeopardy. The exception would be when the judge finds prosecutors intentionally provoked a mistrial.

But the prosecutors pointed out the sudden ending to Clemens’ trial came only on the second day of evidence in what was supposed to be a four- to six-week case. It came before prosecutors called crucial witnesses such as Brian McNamee, the pitcher’s longtime trainer, who said he injected Clemens with steroids and human growth hormone, or showed their key physical evidence — needles McNamee said he used to inject Clemens and which the prosecutors said contained Clemens’ DNA and traces of the drugs.

The defense planned to dispute both vigorously, arguing that McNamee is a habitual liar who fabricated the evidence to blackmail his former boss. But jurors only had hints of that dispute in opening arguments.

“It is impossible to credibly assert that the government had a motive for derailing defendant’s prosecution because it believed the case was going badly when the case was barely going,” the prosecutors said.

Clemens, who has steadfastly denied using performance-enhancing drugs during a 24-year career in which he broke multiple records pitching for the Boston Red Sox, Toronto Blue Jays, New York Yankees and Houston Astros, was the most prominent player accused of using drugs in a December 2007 investigative report to Major League Baseball led by former Sen. George Mitchell.

Clemens went before a House committee in February 2008 to fight the allegations. He is charged with lying under oath by telling lawmakers he never used the drugs.