LONDON, Aug 25 (Reuters) - Space, stars and taboo sex will be on display in Venice this week as the world's oldest international film festival fights to keep its head above water in a city slowly slipping into the sea.
The 70th Venice Film Festival will try and see off competition from increasingly popular extravaganzas in Rome and Toronto by opening with the world premiere of 3D space fantasy "Gravity", starring George Clooney and Sandra Bullock.
Directed by Mexico's Alfonso Cuaron, of "Children of Men" and Harry Potter-sequel fame, the film depicts Bullock and Clooney as astronauts cast adrift after disaster strikes their shuttle.
"I think the main theme of Venice is that it is proving it is not letting Toronto take the wind out of its sails," Jay Weissberg, film critic for trade publication Variety, told Reuters in a telephone interview.
"The number of English-language films is phenomenal and the Rome festival hasn't hurt it at all."
Big names appearing in films vying for Venice's Golden Lion include Scarlett Johansson as an alien in "Under the Skin", Zac Efron in "Parkland" set at the Dallas hospital where John F Kennedy was taken after he was shot, and Matt Damon in dystopian fantasy "The Zero Theorem" directed by Terry Gilliam.
Nicolas Cage stars as an ex-convict in the U.S. southern backwoods movie "Joe" while Judi Dench searches for the child she was forced to give up for adoption in "Philomena".
The festival's unlikeliest "star" will be former Iraq-war era U.S. Secretary of Defense Donald Rumsfeld in the documentary "The Unknown Known" that takes its title from his famous maxim about threats we know about, and those we don't.
Rumsfeld does not make any earth-shattering revelations, London-based film promoter Charles McDonald said, but "It is a fascinating look at the man. It's compelling stuff, absolutely," he added.
The prize for tackling the most unfilmable subject will have to go to 21st-century Renaissance man James Franco, whose movie is based on Cormac McCarthy's slim but gruesome novel "Child of God" about a Tennessee backwoodsman who gets his kicks having sex with women's corpses.
"Everything Franco does seems impossible," Weissberg said, adding that the film had been described as "half 'Deliverance' and half Charlie Chaplin".
Considered one of the world's big three film festivals, along with Cannes and Berlin, Venice has struggled to rid itself of a reputation as a high-cost venue for exhibitors.
Italy is represented in competition by a documentary, Gianfranco Rosi's "Sacro Gra", about life tucked away along the ring road around Rome, and Gianni Amelio's "L'Intrepido" about an unemployed man who makes a living taking over the jobs of people who have to be absent for one reason or another.
There is much advance interest in Taiwan Chinese director Tsai Ming-Liang's "Jiaoyou" ("Stray Dogs") about a father and his two children who eke out an existence in modern Taipei, and their visitation by a strange woman.
Israeli director Amos Gitai's "Ana Arabia" tells the story of a young woman journalist who visits a small, mixed community of Jews and Arabs living together on the outskirts of Tel Aviv.
Gitai, a veteran of the 1973 Arab-Israeli war whose helicopter was shot down by a Syrian missile, is widely respected abroad but divides opinion at home because of his exploration of ethnic and religious tensions.
The festival's jury is headed by veteran Italian director Bernardo Bertolucci, best known for his steamy 1972 movie "Last Tango in Paris" starring Marlon Brando and Maria Schneider
(Editing by Andrew Heavens)