BRASILIA, March 27 (Reuters) - Brazil's Congress will likely move forward with a special investigation of state-run oil company Petroleo Brasileiro SA, the Senate's leader said on Thursday in a move that could impair President Dilma Rousseff's chances for re-election.
A proposal from opposition lawmakers to investigate the controversial purchase of a Texas refinery approved in 2006 by Petrobras, as the company is known, currently has 28 pledges of support, more than needed for formal approval.
Senate President Renan Calheiros indicated he was not in favor of the investigation, but said that given the number of pledges in its favor, "there is nothing else to be done."
"Obviously in an electoral year an investigative committee hinders more than it helps," Calheiros said.
The committee would investigate Petrobras' alleged overpayment for the Pasadena refinery. Brazilian auditors have questioned the $1.2 billion Petrobras paid for it between 2006 and 2012, suggesting the refinery had a market value of less than $50 million.
Rousseff has not been accused of wrongdoing, but she did chair Petrobras' board when the purchase was approved. She has said the decision to buy the refinery was based on a "flawed" and "incomplete" executive summary.
The investigation is likely to give her opponents in the campaign ammunition to argue that she has not been a competent steward of state-run companies or the broader economy.
Rousseff's most likely rivals in the Oct. 5 election, Senator Aecio Neves of the main opposition party PSDB and Pernambuco state Governor Eduardo Campos have both called for a congressional inquiry into the refinery purchase.
A Thursday poll showed support for Rousseff has faltered amid slow economic growth, high inflation and the scandal, although she is favored to win a second term.
(Reporting by Maria Carolina Marcello; Writing by Caroline Stauffer; Editing by Tom Brown)