MILAN, July 26 (Reuters) - Jane Campion"s "The Power of the Dog", Pedro Almodovar"s "Parallel Mothers" and Kristen Stewart"s turn as Princess Diana in "Spencer" are among the titles vying for the top prize at this year"s Venice film festival, which runs Sept. 1-11. The world"s oldest film festival, regarded as a showcase for Oscar contenders as awards season approaches, hopes to welcome back Hollywood celebrities this year after a scaled-down 2020 edition. New Zealand filmmaker Campion, known for "The Piano", will present her drama starring Benedict Cumberbatch as a sadistic ranch owner who launches a campaign against a young widow, interpreted by Kirsten Dunst, in 1920s Montana. A Netflix production, "The Power of The Dog" had been invited to screen out of competition at the Cannes festival but opted instead for Venice, which unlike its French rival does not demand a theatrical release for films vying for the top prize. Spain"s Almodovar reunites with one his favourite actresses, Penelope Cruz, in "Parallel Mothers", while "Spencer", by Chilean director Pablo Larrain, film centres on a weekend in the early 1990s when Diana decided to separate from Prince Charles. They are among 21 films in the main competition, which include Maggie Gyllenhaal"s directorial debut "The Lost Daughter", based on an Elena Ferrante novel, and the "The Hand of God" by Paolo Sorrentino - one of five Italian titles seeking to scoop up the Golden Lion top award. Ridley Scott"s medieval epic "The Last Duel", starring Matt Damon, Adam Driver and Ben Affleck, and Denis Villeneuve"s hotly anticipated science-fiction tale "Dune", with Timothée Chalamet and Zendaya, will both premiere in Venice out-of-competition. Festival director Alberto Barbera hailed the return to the Lido waterfront of "of U.S. studios and of A-list stars who last year were a little wanting". He told a virtual news conference the quality of films this year was higher than usual, and the line-up featured several films lasting three hours or more, some disturbingly violent scenes and many stories with strong women characters. "It"s as if the pandemic helped stimulate creativity all around," he said. With contagion rates on the rise again, anti-COVID restrictions imposed last year will remain in place, including the capacity of festival theatres which has been halved to 4,000 viewers.