George Clooney explores the dirty side of politics in The Ides of March, the opening movie at the Venice film festival in which an aide to a Democratic presidential candidate learns how dispensable ideals can be.

The Hollywood heartthrob directs and acts in the behind-the-scenes look at a U.S. election race, and the world premiere on Wednesday ensures a star-studded red carpet to kick off the 11-day cinema showcase in the canal city.

There was muted applause at the press screening ahead of a photocall, news conference and interviews for the drama in which Ryan Gosling plays the central role of press attache Stephen Myers.

A devoted employee to Clooney's governor Mike Morris, he becomes embroiled in a high-stakes game of sex, power and horse-trading in a critical look at the reality behind political rhetoric.

For all his fine words, Morris emerges as a morally ambivalent figure under pressure to compromise in order to stay ahead in the race.

Oscar-winner Philip Seymour Hoffman plays Myers's boss and Paul Giamatti his rival, and Evan Rachel Wood rounds off the main cast as an intern with a dangerous secret.

The Ides of March takes its inspiration from Beau Willimon's play Farragut North, itself loosely based on the 2004 Democratic primary campaign of Howard Dean.

It is Clooney's latest directorial foray into the world of politics following 2005's black-and-white Good Night, and Good Luck which also launched in Venice.

While it may prove popular in a city where the 50-year-old is a firm favorite and movies critical of America tend to strike a chord, its reception in the United States where it hits theatres in October is less certain.

MADONNA, POLANSKI, SODERBERGH IN LINEUP

The evening gala screening marks the opening of the August 31-September 10 event, which promises eagerly awaited movies and A-list stars who will hope the prestigious launch puts them in the frame for awards next year.

Thousands of journalists and fans have descended on the Lido island across the water from Venice to catch a glimpse of their idols and bring the glamour of the world's oldest film festival to a global audience.

The roll call of celebrities expected this year includes Clooney, Colin Firth, Keira Knightley, Matthew McConaughey, Kate Winslet, Matt Damon, Jude Law, Gwyneth Paltrow and pop superstar Madonna.

It marks a significant turnaround for director Marco Mueller, who was criticized last year for a low-key festival and faces growing competition from the annual rival event in Toronto which overlaps with Venice.

Among the hotly anticipated titles is Tinker, Tailor, Soldier, Spy, an adaption of John Le Carre's spy novel starring recent Oscar winner Colin Firth and Gary Oldman.

Other standout titles in competition include Briton Andrea Arnold's take on the Emily Bronte novel Wuthering Heights, U.S. director Ami Canaan Mann's Texas Killing Fields and William Friedkin's Killer Joe.

In A Dangerous Method, Canadian David Cronenberg explores the rivalry between Carl Jung and Sigmund Freud as a young woman (Knightley) comes between them.

Roman Polanski worked on the screenplay for his latest movie Carnage, featuring Winslet, Jodie Foster and Christoph Waltz, while under house arrest in Switzerland last year.

Russian director Alexander Sokurov brings Faust and Hong Kong's Johnnie To presents Life Without Principle, a story touching on the economic crisis and its effect on ordinary people.

Outside the main lineup, Madonna makes her second feature film W.E., a drama loosely based on divorcee Wallis Simpson whose relationship with Britain's King Edward VIII led to his abdication in 1936.

Steven Soderbergh promises an all-star cast including Damon, Winslet, Marion Cotillard, Law and Paltrow in Contagion, about a lethal airborne virus that spreads panic.