CANNES, FRANCE: Sean Penn may be president of the Cannes Film Festival jury — but don't expect any buttoned-up presidential behavior from the Hollywood rebel.

During a news conference on opening day Wednesday, the actor-director lit up two cigarettes in defiance of French laws against smoking in public buildings. He used the F-word. And he poked fun at his reputation.

Asked by a reporter if he could confirm that he had hesitated before taking the jury presidency because it means being ''wise and sober'' for 12 days, the Into the Wild director quipped, ''How many days have I got left?''

Penn, a regular at Cannes, won the best actor award here for She's So Lovely, and he showed his own movies The Pledge and The Indian Runner here. When Clint Eastwood's Mystic River played at Cannes, it generated early buzz for Penn's performance, which went on to win an Academy Award.

Penn wasn't all jokes and antics at Cannes — he also let his serious, thoughtful side shine through, urging reporters to see a documentary that the festival included at his special request. The Third Wave is Alison Thompson's look at volunteers who joined relief efforts in Sri Lanka after the 2004 tsunami.

''I thought that it was the closest thing that I had ever seen on film to giving any kind of answer to 'what's the purpose of life?' — at least for those who might be lucky enough to have two good legs and a dollar in their pocket,'' he said.

Penn also talked politics, saying that he's not supporting any particular candidate in the U.S. presidential election, though he is ''encouraged by the kind of exciting support that Barack Obama has.''

As he often does, Penn railed against President Bush. Asked about Bush's politics, he said the choice of the word ''politics'' was unfortunate. ''It's just a shame that we have to bastardize the term 'politics' in attributing it to people like that, because politics, again, should really be an organization of helping each other,'' he said.

Over the almost two-week festival, Penn will lead a jury made up of director Alfonso Cuaron (Children of Men), actress Natalie Portman (V for Vendetta), comic book artist-filmmaker Marjane Satrapi (Persepolis), actor-director Sergio Castellitto (My Mother's Smile), actress Jeanne Balibar (Clean), director Apichatpong Weerasethakul (Tropical Malady), director Rachid Bouchareb (Days of Glory) and actress Alexandra Maria Lara (Downfall).

The winners will be announced May 25.