By Jeremy Pelofsky

WASHINGTON (Reuters) - Security officers at a U.S. courthouse are under investigation for receiving baseballs autographed by former pitching ace Roger Clemens, who faces perjury charges, the U.S. Marshals Service said on Tuesday.

Clemens, who played for four Major League Baseball teams and won the Cy Young Award for best pitcher seven times, went on trial last month on charges of lying to Congress in 2008 when he denied taking steroids and human growth hormones.

A mistrial was declared after two days.

The security officers at the federal courthouse in Washington, where Clemens is being tried, are contractors from Inter-Con Security which launched a probe at the request of the Marshals Service after learning of the allegations last week.

"The contractor's investigation is ongoing but preliminary results indicate that up to six baseballs were given to a contracted court security officer and were distributed among four or five other court security officers," said Jeffrey Carter, a Marshals Service spokesman.

He said that it was a violation of the contract, valued at $5.2 million annually, to accept gifts in connection with official duties. The investigation was first reported by the Washington Post.

There is no indication that U.S. Marshals, who also provide and oversee security at federal courthouses, received any of the memorabilia from the Clemens defense team, Carter said.

The former baseball star's lead defense attorney, Rusty Hardin, was not immediately available for comment. A representative for Inter-Con Security also was not immediately available for comment.

Judge Reggie Walton declared a mistrial in the Clemens case on July 14 after prosecutors violated his order to exclude certain information from the proceedings.

Clemens's attorneys have urged Walton to dismiss the charges, saying that prosecutorial misconduct should bar another trial. They argued that another trial would violate his constitutional right against being tried twice on the same charges. Prosecutors are due to respond by Friday.

(Editing by Paul Simao)