* Opposition wins 272-199 in controversial vote
* Secret ballot reveals deep splits in key gov't ally PMDB
* Veteran lawmaker in graft probe reportedly opts for plea (Add comments by lawmaker and analyst, political context)
By Anthony Boadle
BRASILIA, Dec 8 (Reuters) - The lower house of Brazil's Congress voted on Tuesday to appoint a committee stacked with opponents of President Dilma Rousseff to study whether to impeach her for breaking budget rules, a blow to the leftist leader battling for political survival.
In a secret ballot, lawmakers voted 272-199 for a list of committee members drawn up by the opposition and pro-impeachment members of the centrist Brazilian Democratic Movement Party (PMDB), the biggest party in Rousseff's governing coalition.
It was a clear defeat for Rousseff in the first battle of an impeachment process started last week that threatens to paralyze Congress for months, distracting policymakers from Brazil's worst recession in decades.
The vote was also a slap in the face for the leader of the PMDB party in the lower house, Leonardo Picciani, who has backed Rousseff since she appointed two ministers from his wing of the party to secure support and fend off impeachment.
Picciani's loss of face in the high-profile secret vote underscored the deep divisions within his party, which has veered away from the government in recent months as the economy plunges and a vast corruption scandal rattles the capital.
The sweeping investigation into bribery at state-run oil company Petroleo Brasileiro SA threatened to further strain Rousseff's fragile coalition on Tuesday, as a veteran lawmaker in jail was reported to have decided to negotiate a plea bargain.
Senator Delcídio do Amaral, President Dilma Rousseff's point man on economic affairs, hired a lawyer to write up a plea deal, reported the websites of newspaper Folha de Sao Paulo and news magazine Veja, without saying how they got the information.
Amaral and billionaire Andre Esteves, the former controlling shareholder and chief executive of investment bank BTG Pactual SA, were arrested last month and accused of obstructing the probe into the oil giant known as Petrobras.
House Speaker Eduardo Cunha, who has been charged with corruption and money laundering in the Petrobras probe, outflanked Rousseff's allies with Tuesday's secret vote and postponed an ethics hearing into his activities for another day.
Amaral, Esteves and Cunha have denied any wrongdoing. Lawyers for Amaral could not immediately be reached following the reports of a plea deal.
While the result was hard blow for Rousseff, the fact that 199 lawmakers voted for the pro-government list was a sign that she may still have the more than one-third of support needed to block an eventual impeachment vote before the full house.
Her supporters in Congress plan to appeal to the Supreme Court against the secret voting procedure adopted by Cunha, who allowed the alternative list to be presented.
Controversy over the vote descended into chaos on the floor of the house, as some lawmakers outraged by the secret vote smashed an electronic voting urn and unplugged others, while pro-impeachment parties waved a flag in celebration of the win.
"The result shows that the government is in a delicate situation," the political consultancy Arko said in a note to clients.
The committee, whose final members should be named on Wednesday, will have the task of reporting on whether Rousseff committed an impeachable offense.
Opponents who filed the impeachment request that set the process in motion accuse her of breaking budget rules to boost spending during her re-election campaign last year. Rousseff has denied any taking any illegal measures.
If the committee finds an offense was committed, the process will go to a full vote on the house floor. The opposition needs two-thirds of the votes to begin a 180-day impeachment trial in the Senate. During that trial the president would be suspended and replaced by her vice president, Michel Temer of the PMDB.
Speculation mounted on Tuesday that Temer was preparing for that scenario after publication of a letter he sent Rousseff on Monday complaining that she had sidelined him and his party in her government. (Reporting by Anthony Boadle; Editing by Frances Kerry and Cynthia Osterman)