LOS ANGELES (Reuters) - Lawyers for film-maker Roman Polanski have launched a new bid to have the Oscar winner's 37-year-old child sex case closed, which would allow The Pianist director to travel freely without the threat of extradition.

His attorneys filed a motion on Monday in Los Angeles Superior Court seeking a hearing next month where they would ask to submit evidence in the hopes of proving that the 81-year-old director has been subjected to "false" extradition requests by the United States authorities. "The true facts and circumstances surrounding Polanski's term of incarceration and his decision to leave the country in 1978 resulted directly from judicial and prosecutorial misconduct and should no longer be covered up," Polanski's attorney Bart Dalton wrote in the motion.

High-profile lawyer Alan Dershowitz has also asked the court for permission to represent Polanski.

The film-maker was charged in 1977 with raping a 13-year-old girl in Los Angeles after plying her with champagne and drugs. He later pleaded guilty to having unlawful sex with a minor.

But the director of Rosemary's Baby (1968) and Chinatown (1974) fled the US to France before sentencing, fearing the judge would impose more prison time than the 42 days he had spent behind bars for a psychiatric evaluation.

Lawyers for Polanski, who has a warrant in the US for his arrest, believe that he has served his sentence and that he must not be physically present in court for the case to officially close.

His lawyers have fought for years to have the case thrown out on claims that he was a victim of judicial and prosecutorial misconduct, issues the courts have ruled that they cannot address unless he returns to California.

A spokesman for the Los Angeles District Attorney said the office had no comment on the motion.

Polanski was questioned by Polish prosecutors in October after the US authorities requested his extradition.

The motion says prosecutors "deliberately omitted" the time Polanski served in prison in an extradition request as a way to meet the criteria of a US-Poland treaty.

In 2009, he was held for 290 days under house arrest in Switzerland as the authorities considered whether to extradite him to the US.

Polanski, who spent much of his young life in Poland, has said that he plans to shoot a film about Alfred Dreyfus, a Jewish French military officer falsely convicted of treason, in Poland.