By Brian Winter
SAO PAULO, May 29 (Reuters) - Police in Brazil's biggest city are seeking to arrest and jail a hard core of violent street protesters before the World Cup starts in two weeks, using wiretaps and other surveillance in an effort to prevent clashes from spoiling the tournament.
Fernando Grella, the head security official for Sao Paulo state, told Reuters that police are assembling possible criminal cases against a small number of protest leaders, perhaps a few dozen, who he said are conspiring to "commit violent acts, break things, vandalize and attack people."
The intelligence work is not yet complete so it's unclear whether prosecutors will agree to bring charges that would result in so-called "preventive arrests," Grella said.
The likelihood of violent protests is one of the biggest concerns for Brazil's government and world soccer body FIFA as the World Cup gets ready to kick off in Sao Paulo on June 12.
Brazilians angry over public money being spent to host the tournament, among other grievances, have been staging periodic demonstrations for a year now. While most protesters have been peaceful members of the middle class, several marches have resulted in clashes with police and vandalism that officials blame on a small number of students and other youths.
The "intense intelligence operation" described by Grella is one of the most extensive yet disclosed by Brazilian security forces. While federal agencies are also gathering information on protesters, it's unclear if police in the other 11 cities that will host games are also seeking preventive arrests.
Grella said police have used video surveillance and internal records to identify the most violent protesters and, in some cases, have tapped their phones and monitored their social media use and e-mail traffic.
The objective, he said, is to identify cases of premeditated, organized violence that would constitute "criminal association" - a charge akin to conspiracy that is more typically used against organized crime groups here.
If prosecutors agree to press charges, some protest leaders could be immediately arrested and jailed for a period of a few days or longer, he said.
"We're doing preventive policing that seeks to guarantee people's right to protest and freedom of expression, while at the same time seeking to channel these events in a way that they disturb daily life as little as possible and avoid violent acts," Grella said.
He said building a case against the protesters was "difficult, but not impossible."
"I'd like to believe that ... in the next few weeks we will have some arrest warrants," he said.
Two senior sources with Brazil's public ministry, an independent judicial body that would likely have to approve criminal charges against protesters, said they were skeptical that conspiracy charges would apply.
Esther Solano, a university professor who has studied the protests over the past year, said they are generally leaderless and loosely organized, making it difficult for police to identify potential troublemakers.
"What (police) are trying to do seems excessive," she said. "It shows you how much pressure police and politicians are under to avoid a big mess during the World Cup."
The justice ministry, which oversees police nationally, did not immediately respond to a request for comment.
Asked if protests could be bigger than those that drew hundreds of thousands of people onto the streets last June during the Confederations Cup, a warm-up event for the World Cup, Grella said: "It's difficult to say."
He said, however, that June 12, when Brazil's team will play Croatia in the tournament opener, "is the day that most worries us" in terms of demonstrations.
Grella praised federal and other state agencies for sharing security-related information prior to the Cup. He also said he had received no indications of a particular threat from international terrorists or Brazilian organized crime groups. (Editing by Kieran Murray)