Other filmmakers at the festival, including French New Wave director Jean-Luc Godard and actor-director Mathieu Amalric, have signed the petition, which is posted on a Web site overseen by renowned French philosopher Bernard-Henri Levy.
Polanski was taken into custody in September and is currently under house arrest in Geneva.
The interview aired hours before British actress Charlotte Lewis claimed at a news conference in Los Angeles that she was sexually abused by Polanski in 1982 when she was 16.
Polanski pleaded guilty in 1978 to unlawful sexual intercourse with a 13-year-old girl. But after a judge said he would renege on the plea bargain, Polanski fled to his native France. He has been a fugitive since then.
In the interview with RTL radio broadcast on Friday, Douglas said Polanski had been given "some bad advice" when the scandal broke.
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