A seven-member jury led by German director Werner Herzog ("Fitzcarraldo") and including Oscar-winning actress Renee Zellweger are to crown the best of 20 features vying for the coveted award at a glittering ceremony on Saturday evening.
A critics' poll in industry magazine Screen showed the Polanski film neck-and-neck with the Russian drama "How I Ended This Summer", set at a remote Arctic weather station, and "If I Want to Whistle, I Whistle" about the inmates of a grim Romanian youth prison.
A separate survey of German reviewers in the Berlin daily Der Tagesspiegel also showed the three pictures faring well in a strong year for eastern European film-making.
Polanski missed out on the world premiere of his picture at the Berlinale, the first major international cinema showcase of the year, due to his house arrest in Switzerland for having sex with a 13-year-old girl in 1977.
But critics showered the movie with praise, calling it a return to form for the 76-year-old French-Polish film-maker, best known for classics such as "Rosemary's Baby" and "Chinatown".
"Mr. Polanski is a master of menace," New York Times critic Manohla Dargis said in a glowing review Friday for the film's US release. "He creates a wholly believable world rich in strange contradictions and ominous implications. He's delivering the pulpy fun at such a high level that
'The Ghost Writer' is irresistible, no matter now obvious the twists."
The picture, based on Robert Harris' best-seller "The Ghost", features a stand-out performance by Pierce Brosnan as a former British prime minister modelled on Tony Blair being probed for war crimes over the torture of terror suspects.
He hires a ghost writer (Ewan McGregor), who remains nameless throughout the movie, to shape up his memoirs but the hired scribe soon stumbles upon a deadly web of transatlantic political intrigue.
"How I Ended This Summer" is the second solo feature film for Russia's Alexej Popogrebski, 37, tracks two men working at an island polar station, an intern and an experienced meteorologist.
When the intern is given the message that his colleague's wife and child have been killed on the mainland, he makes a fateful decision to withhold the news.
"It starts off at near glacial pace and then rolls to a suspenseful boil without ever resorting to cheap thriller tricks," Variety magazine said, praising the film's stunning landscapes and restrained performances. "The picture just works as a terrific exploration of human fragility."
"If I Want to Whistle, I Whistle" is the debut feature by Florin Serban, a 35-year-old film-maker who is riding a wave of international acclaim for young Romanian cinema. His cast is made up primarily of amateurs, including George Pistereanu, a Bucharest high school student who went through intensive drama training to play a tormented delinquent.
"Pistereanu moves beyond the stubborn rebelliousness of his character to convey intuitively not only the vulnerability but also the despondency of an 18-year-old who has not yet learned the meaning of the word 'consequences'," Screen critic Dan Fainaru wrote.
But Berlin prizes are notoriously unpredictable and respected entries such as "Honey" from Turkey or the Bosnian contender "On The Path" could also triumph. The Berlinale, which wraps up Sunday, is the only one of the top European film festivals that allows the general public to attend.
This year saw record box office returns with 270,000 tickets sold in the first week of the 11-day event.