By Stuart Grudgings

RIO DE JANEIRO, Aug 28 (Reuters) - Militias run by corrupt police in Rio de Janeiro are likely to become more violent as they clash with each other and take on traits of the drug gangs they ejected from many slums, an expert said on Thursday.

The militias, some linked to senior state politicians, have taken control of dozens of poor communities in Brazil's tourist capital, where they extort money in protection rackets, run illegal businesses and deal out summary justice.

There is evidence of growing rivalries between militia groups and their involvement in the cocaine trade, said Ignacio Cano, a professor at Rio State University who released one of the first detailed studies of militia groups on Thursday.

"This could lead into open fighting with different militia groups just as the drug networks do. If that happens, the level of violence is going to rise dramatically," Cano told Reuters.

Cano said nearly 3,500 accusations against militias have been registered on the city's anonymous complaints telephone line since the end of 2006, with extortion the most common at 20 percent of the total and drug trafficking at 5 percent.

The end of 2006 saw a surge of militia "invasions" of communities to oust drug gangs. The groups were broadly welcomed by the media and senior politicians at the time for combating the drug trade.

But the mood turned against them after one militia group tortured some local journalists in May and several politicians have been arrested in recent months on suspicion of running militias. A militia calling itself the League of Justice is accused of shooting dead at least seven innocent residents last week in a western area of Rio.

Among 46 residents in militia-controlled areas interviewed by Cano's research team, several said the militias's punishment of residents was similar to the drug gangs' tactics -- physical violence, expulsion from the community, and murder.

"It's the same thing, just worse because the drug gangs don't charge you," said one unidentified resident.

Cano said the militias were in some ways a more entrenched problem than the drug gangs because they were effectively a part of the state. Despite recent arrests of suspected militia leaders, he said the only way to deal a serious blow to their operations would be for police to reoccupy the slums.

"It's difficult to expect the state is going to act against them. It does happen but they have ways to protect themselves because they have the information and they are starting to threaten policemen who are doing the investigations," he said. (Editing by Todd Benson and Kieran Murray)

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