Roman Polanski's sex assault victim has told a judge to drop the 40-year-old case against the Oscar-winning director as an "act of mercy" to end her decades of suffering.

Samantha Geimer, 13 at the time of the attack, has long publicly supported the demise of the saga, but it is the first time she made the plea to a judge.

Ms Geimer, now 54, told Los Angeles Superior Court that she believes Polanski served his time when he spent 42 days in jail before he went on the run.

She said: "I would implore you to consider taking action to finally put this issue to close as an act of mercy to myself and my family.

"I would like to ask you to consider sentencing Mr Polanski to time served in absentia.

"I know Roman's family has suffered as well - we are human beings.

"A 40-year sentence has been imposed on the victim of the crime as well as the perpetrator.

"Justice is not only about punishment, it's about equity and consideration."

Ms Geimer, whose blonde bob was highlighted with a streak of pink, appeared in court alongside her husband David to make the motion which was supported by Polanski's lawyer, Harland Braun.

She said she is now a grandmother and wants to end the media intrusion that she believes exists because the case is not settled.

But Deputy District Attorney Michele Hanisee rejected the victim's motion to dismiss the case, arguing that it is in Polanski's hands to return to the country to end the ordeal.

"It's not the people (state) who have caused her continued suffering," she said.

Judge Scott Gordon said he would respond in writing and thanked Ms Geimer for her bravery.

"You are an elegant and courageous testament to the fact that sexual assault not only impacts the victim at the time," he said.

Polanski, 83, has been in self-imposed exile for nearly four decades after pleading guilty to having unlawful sex with Ms Geimer at actor Jack Nicholson's Hollywood hills home in 1977.

The fugitive, currently living in France, admitted the lesser of six charges, the rest being dropped, after allegedly plying the teenager with champagne and a portion of a sedative pill during a photo shoot.

They are trying to get an Interpol arrest warrant lifted so his movement is not restricted to France, Switzerland and Poland, where he fled the Holocaust.

Mr Braun claims the case is no more than a "political circus" and that Polanski has already served his time by spending more than 300 days in jail and house arrest in Switzerland during a failed extradition attempt seven years ago.

Polanski, who won a best director Oscar for The Pianist, fled in 1978, fearing a judge would extend his sentence after he spent 42 days in jail.

Nicholson was not at home at the time of the offence and prosecutors dropped charges of rape and sodomy against Polanski.