By James Mackenzie and Laura Viggiano

ACERRA, Italy (Reuters) - Acerra, in southern Italy, has long suffered abnormally high rates of cancer, apparently linked to the illegal waste dumps that dot the surrounding countryside, and something of their toxic effect has seeped into political life as well.

Campaigning for local elections on Sunday and Monday has been marked by a series of incidents that have highlighted the pervasive corruption hindering efforts to clean up the system in the sprawling Campania region around Naples.

"I was going home at lunchtime. It was raining quite heavily and a couple of people in covered motorcycle helmets pulled up, banged on my car window with a pistol butt and told me to stop campaigning and drop it," said Andrea De Chiara, a candidate in the election.

In the homeland of the Camorra, Naples' version of the Mafia, the obvious suspect is organized crime. DIGOS, the special police unit that handles public order and terrorism cases, has joined the investigation.

However people who know the area, including police officials and De Chiara's Italia Popolare party itself, are wary of blaming the mob and say the danger is more insidious.

They say a serious threat would be more specific and less crudely obvious and smaller local gangs or business interests, possibly operating in the shadow of the Camorra and interested in making politicians keep quiet, are more likely suspects.

"This is people muddying the waters. This is not what a serious threat looks like," said Raffaele Tagliamonte, director of the local television station and president of the Acerra Lions Club, who himself received an anonymous letter warning him to stay out of the campaign.

In Acerra, an ancient, nowadays slightly scruffy town of 52,000 inhabitants with a plant that supplies electricity to the Fiat works in nearby Pomigliano, there are many potential interests at stake that do not involve organized crime directly.

More than 500 candidates are running in a mixture of coalitions and the flyposters busy papering over the signs of rival parties are testimony to the fevered politics of the campaign.

There are building permits to be assigned, environmental issues to be sorted out and millions of euros to be allotted to deal with the perennial waste management problem.

The fact that whoever was behind the threat targeted Italia Popolare, a small local party with no important public offices or contracts to hand out, suggests a more subtle aim.

"In another context, this might be called bullying. It's a way of trying to make you be quiet and mind your own business," said party coordinator Giuseppe del Pennino.

STAY OUT

The intimidation reported in Acerra and other parts of Campania ahead of the election may have been less serious than some of the violent threats seen recently in Calabria, home of the deadly 'Ndrangheta criminal organization, where a pharmacy owned by a local mayor was firebombed.

But whether or not the half dozen or so incidents reported in the town over recent weeks are the work of organized crime or some lower-level interests, they underline the huge challenge facing attempts to change the way Italy works.

If Prime Minister Mario Monti's drive to overhaul the Italian economy is to succeed, it has to succeed in the south, a region that has been a byword for economic stagnation and the crippling power of organized crime for decades.

Unemployment in Acerra runs at around twice the national average at 20 percent and there is deep resentment at the austerity measures imposed by the government in Rome among many who feel the system is already rigged against them.

In such a climate, the unglamorous daily work of local politicians whose decisions can have a big impact on everyday life and on changing the way the state is perceived can be especially difficult.

A pervasive culture of favors and "raccomandazioni" colors even basic interactions, helping people with the right connections avoid fines or taxes but making a well-placed friend a necessity even for such simple tasks as getting a license or official papers.

"People here have seen everything, they're just resigned now. There's very little hope for change," said Mafalda Arrivo, who is running for election in the port of Torre del Greco at the foot of Mount Vesuvius.

In Torre del Greco, the collapse of a local shipping company has hit thousands of families who had invested savings in bonds issued by the group and has added an extra element of bitterness which is likely to further damage trust in institutions.

An energetic and determined-looking woman who is running for the Italy of Values party led by former anti-corruption magistrate Antonio Di Pietro, Arrivo has few illusions about the realities of local politics in her home town.

Abstentions are likely to be high, there are rumors of votes being on sale for as little as 200 euros for a package of seven, and fingers are pointed at the dubious background of some candidates.

Arrivo herself last week found someone had smeared oily muck on a shop she once owned, in an apparent act of intimidation.

"But you can't give up, if only for the sake of your children," she said from the improvised campaign office she has set up above her clothes shop near the town centre. "If you give up, what have you got left?"

(Editing by Giles Elgood)