BRASILIA (Reuters) - The head of Brazil's Senate police was arrested on Friday for counter-intelligence efforts to protect senators implicated in a sprawling graft scandal, even sweeping their homes for bugs, police said.

A statement by Brazil's federal police did not name the senators the officer allegedly sought to protect, but Brazilian media said they included two former presidents, Jose Sarney and Fernando Collor de Mello, and former Energy Minister Edison Lobao.

A lawyer for Lobao confirmed that the senator had recently requested a house sweep but denied any wrongdoing, saying that by law such sweeps are part of the Senate police's job.

Police arrested the official, Pedro Carvalho, and three officers from his force in the Brazilian capital and searched their Senate offices for evidence.

"We have obtained proof that this group, led by the director of the Senate police, was hindering Federal Police investigations of senators and former senators, using intelligence equipment," the statement said.

On one occasion, it said, Carvalho ordered his officers to "intimidate" federal policemen when they arrived to search a senator's apartment with an order from the Supreme Court.

If confirmed, the allegations would underscore longstanding concerns about how Brazil's powerful politicians wield influence to obstruct investigations and avoid prosecution for corruption.

They would also represent another victory for probes linked to "Operation Car Wash," a far-reaching investigation that has made historic inroads against a traditional culture of impunity for Brazil's corporate and political elite.

Now more than two years old, the investigation centers on bribes and political kickbacks from contracts with state-run oil company Petroleo Brasileiro SA, or Petrobras.

The investigation contributed to the recent downfall of the leftist Workers Party after 13 years in power and led to the arrest of dozens of senior executives of major engineering and construction companies.

It also implicated more than 50 politicians, including Sarney, Collor de Mello and Lobao. The three have denied receiving bribes.

Lobao's lawyer, Antônio Carlos Castro, who also represents Sarney, said no bugs were found in the senator's house. The request for a sweep resulted from concerns about the taping of conversations by defendants seeking to incriminate others for plea deals in the Petrobras scandal.

Castro said Sarney, who retired from the Senate in early 2015, had not used the legislative police because he had his own security staff as former president of Brazil. Collor de Mello's office did not return calls.

In charges against Collor de Mello made public this week, prosecutors accused the former president of taking more than 29 million Brazilian reais in bribes between 2010 and 2011 from contracts with Petrobras' distribution unit, BR Distribuidora.

They said Collor, who resigned as president in 1992 before his imminent impeachment for corruption, laundered part of that money by buying luxury cars seized at his mansion in Brasilia last year.

On Wednesday, Eduardo Cunha, the once powerful speaker of Brazil's lower house and leader of the successful impeachment drive against former Workers Party president Dilma Rousseff, was arrested on charges of receiving millions in bribes.

(Reporting by Anthony Boadle; Editing by Steve Orlofsky)