(Adds details of corruption allegations, background)
By Anthony Boadle and Lisandra Paraguassu
BRASILIA, Oct 19 (Reuters) - Eduardo Cunha, the former head of Brazil's lower house of Congress who led the impeachment drive against former President Dilma Rousseff, was arrested on Wednesday on corruption charges.
Cunha, one-time leader of the Evangelical Christian caucus in the House of Deputies is accused of receiving millions in bribes from a purchase of an oil field in Benin by state-run oil company Petrobras, which led to his arrest on Wednesday.
In a separate case before a federal court in Rio de Janeiro, Cunha is also charged with taking $5 million in bribes in relation to contracts for two drillships for Petrobras, which is known formally as Petroleo Brasileiro SA.
Leonardo Cavalcanti, a spokesman for the federal police, said Cunha was arrested in the capital Brasilia. He was flown Wednesday afternoon to the southern city of Curitiba, where he will stand trial before anti-corruption judge Sergio Moro.
Cunha was expelled from the lower house last month in an overwhelming vote by his peers in the chamber. That stripped him of legal protections that effectively give politicians immunity from all courts except the severely backlogged Supreme Court. Judge Moro, by contrast, is known for acting with speed and Cunha's case could be ruled upon before the end of the year.
Brazil's federal prosecutors said in an emailed statement that Moro accepted their request that Cunha be subject to "preventative" arrest. They said there was a risk of Cunha obstructing the investigation and raised "the concrete possibility" he would flee Brazil because of "hidden funds abroad and his dual nationality."
That means that the former congressman, who also holds Italian citizenship, can be held for an indefinite period.
Cunha has said he is innocent. It was not immediately possible to contact his lawyer, who was with him when he was arrested.
Cunha's apprehension is the latest high-profile action in the sprawling investigation into the sprawling graft scheme at Petrobras. Prosecutors say Brazil's biggest construction and engineering firms paid billions in bribes to executives at the oil firm and politicians in return for bloated contracts.
To date, nearly 200 executives and former politicians - including popular former President Luiz Inacio Lula da Silva - have been charged in the Petrobras probe and 83 have been found guilty. Prosecutors are seeking 38 billion reais ($12 billion) in damages from companies and individuals involved.
Cunha is a longtime member of the Brazilian Democratic Movement Party (PMDB) of current President Michel Temer, who served as Rousseff's vice president and took over in May during the impeachment process against her. Cunha in August became the first sitting politician to be charged in the case.
Two sources close to Temer told Reuters that the order at the presidential palace is to remain silent on Cunha's arrest, mainly because of concerns that he may turn state's witness and implicate fellow PMDB politicians, whom Cunha lashed out against for not defending him against the recent criminal charges.
Cunha is a lightning rod of ire for those who opposed Rousseff's impeachment, carried out on the grounds that she broke budgetary rules.
Rousseff and her supporters say she was the victim of a "coup" carried out as an attempt to halt the Petrobras probe - and they pointed to Cunha as the crudest example of that effort.
Federal prosecutors in Curitiba, who have led the Petrobras investigation, have said they will not allow any politician to halt their work - and fought back vocally against scattered attempts by lawmakers to impede their efforts.
(Reporting by Anthony Boadle and Eduardo Simoes; Writing by Brad Brooks; Editing by Daniel Flynn and Alan Crosby)