By James Mackenzie

CANNES, France (Reuters) - A hard-hitting film based on an Italian bestseller made its debut on Sunday, depicting the brutal world of the Camorra, the Naples crime network whose tentacles extend from drugs and waste disposal to haute couture.

"Gomorra", in competition at the Cannes film festival, is based on the bestselling account of Naples' version of the mafia by journalist Roberto Saviano, who has been living under police protection for the past two years.

"In Italy, and I think not just in Italy, there is a hunger for these stories," he told a news conference at which he was loudly applauded by Italian reporters. "We are tired of folkloric or fictionalised images of crime."

The film, directed by Matteo Garrone, is shot in a flat, unshowy style reminiscent of Italy's postwar neo-realist cinema and follows a web of characters from teenaged gunmen in the run-down suburbs of Naples to a sleek politician arranging to dump toxic waste illegally.

Due to open in Italy this week, the film comes just weeks after television images of rubbish piled in the streets provided a stark illustration of the extent of the Camorra's grip on the Naples economy.

But the project has also caused controversy in Italy, where Saviano has been accused of washing dirty linen in public and defaming Italy's good name abroad.

He said he had grown used to the accusations but said it was important not to hide the truth of a story which had a resonance well beyond one country.

"I think that this very silence, which is often in our country's tradition, is a way of vilifying our country, which is why telling the story is necessary," he said.

"I don't think Matteo or the others ever thought of denouncing or shouting but just telling the story."

With a soundtrack made up largely of the sugary pop songs blaring out of radios and filmed in desolate apartment blocks and vacant ground at the edges of the city, the film is a vivid portrait of bleak and violent lives.

It shows a boy moving from delivering groceries to carrying drugs, a tailor heading a workshop turning out skilfully made haute couture knock-offs or two teenagers aping Al Pacino's cinema gangster "Scarface" before they anger a local boss and are coldly eliminated.

One of the images that keeps reappearing is hands counting bundles of euros and the sheer scale of the criminal world examined by the film is staggering.

With profits from drug dealing, protection rackets and prostitution recycled into legitimate investments like real estate, its impact stretches far beyond the mean streets of Naples but violence is never far off.

"We are talking about an economy worth 150 billion euros a year, we are talking about an organisation that in less than 30 years has killed 10,000 people," Saviano said.