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VENICE (Reuters) - Brad Pitt and George Clooney star in a madcap comedy by the Coen brothers in which two gym employees get caught up in the cloak-and-dagger world of international espionage, with results both daft and deadly.

"Burn After Reading" -- spy movie meets slapstick farce -- ensured an upbeat opening to this year's Venice film festival, which opened on Wednesday and winds up in 11 days' time.

Hundreds of screaming fans lined the entrance to the main cinema on the Lido waterfront to greet the Hollywood heartthrobs, who signed autographs and joked with the public before taking their seats for the world premiere of the film.

It re-unites Joel and Ethan Coen with actress Frances McDormand, who is married to Joel and who won an Oscar for her role in their 1996 film "Fargo", as well as with Clooney, who appeared in "O Brother, Where Art Thou?"

Clooney, by his own admission, regularly plays the fool for the brothers, fresh from their triumph at this year's Oscars where "No Country For Old Men" picked up four awards, including best picture and best directing.

"I've done three films with them and they call it my trilogy of idiots," the actor told reporters after a press screening.

The 47-year-old plays a nervous, twitchy federal marshal whose extra-marital affairs bring him into contact with a gym instructor, played by Pitt, desperately seeking to extort money from a sacked CIA analyst whose memoirs go missing.

"After reading the part, which they said was hand-written for myself, I was not sure if I should be flattered or insulted," said Pitt, whose character the directors describe as a "knucklehead".

Joel Coen said he and his brother had "a long history of writing parts for idiotic characters.

"By the way, I'm starting to detect something in the crowd here, a feeling that you all feel there's something wrong with being an idiot. I just want to caution you about that, because that's a sensitive subject and a big demographic."

A-LIST AND ARTHOUSE

Although there are five U.S. films in the main competition lineup of 21, they represent "independent" cinema as opposed to the big studios, which are not in Venice this time around.

"Burn After Reading" is not in competition, but U.S. films in the main lineup include "Rachel Getting Married", directed by Oscar-winner Jonathan Demme and starring Anne Hathaway and Debra Winger, who has been nominated three times for an Academy Award.

Kathryn Bigelow directs Iraqi drama "The Hurt Locker", a year after Brian De Palma's "Redacted" stunned audiences in Venice with its brutal reconstruction of events from the war.

Mickey Rourke stars in Darren Aronofsky's "The Wrestler" while acclaimed Mexican screenwriter Guillermo Arriaga makes his directorial debut with "The Burning Plain" starring Oscar winners Charlize Theron and Kim Basinger.

Japan has three main competition entries, led by revered animation director Hayao Miyazaki whose "Ponyo on the Cliff by the Sea" is already storming the box office at home.

Other highlights include "Valentino: The Last Emperor", about the celebrated Italian designer's last two years at the helm of the fashion house he created, and a film about the tumultuous love life of composer Giacomo Puccini.

The 65th Venice film festival is dedicated to the late Egyptian director Youssef Chahine, who died in July aged 82, and is also honoring Manoel de Oliveira, the Portuguese film maker who is still going strong at 99.

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