Clooney stars in and directs the movie Good Night, Good Luck

Clooney plays a principled CBS TV producer, Fred Friendly, during the McCarthy era of the early 1950s.

Ang Lee's gay cowboy film Brokeback Mountain starring Heath Ledger and Jake Gyllenhaal is also tipped by festival-goers as a strong contender.

A total of 19 films are competing for the Golden Lion, including British film The Constant Gardener.

The romantic thriller starring Rachel Weisz and Ralph Fiennes and directed by Brazilian Fernando Meirelles is taken from the novel by John le Carre.

It tells the story of one man's quest to uncover the truth behind a personal loss and a far more wide-ranging conspiracy.

Films from countries including the US, Russia, Italy, China, France, Portugal and Japan are competing for the Golden Lion as the 11-day annual festival winds up on Saturday night.

Sir Anthony Hopkins and Jake Gyllenhaal star in Proof

Other films vying for the award include Proof from British director John Madden and starring Sir Anthony Hopkins, Gwyneth Paltrow and Jake Gyllenhaal.

Based on the Pulitzer Prize-winning play by David Auburn, Proof sees Paltrow return to a character she first played on the West End stage in 2002.

The Brothers Grimm, the first film in seven years by director Terry Gilliam, is also up for the award.

The film stars Heath Ledger and Matt Damon and is a fantasy about a pair of con-merchants in 18th Century Germany which incorporates many of the famous Grimm fairytales.

Other awards will also be handed out at the closing gala including those for best actor and best actress.