By Anthony Boadle

BRASILIA, March 12 (Reuters) - The rift between President Dilma Rousseff and her main political allies widened on Wednesday one day after they voted in Congress to look into bribery allegations leveled at Brazil's state-run oil company Petrobras.

Disgruntled congressmen from coalition parties summoned an array of Rousseff's cabinet members to appear before various congressional committees in a new display of discontent.

They also invited Maria das Graças Foster, the chief executive officer of state-controlled oil producer Petróleo Brasileiro SA, to answer questions about the allegations that a Dutch company paid bribes to company officials to win contracts for floating oil platforms.

The revolt in the ranks of the ruling coalition is led by Brazil's largest party, the center-right PMDB, which is jockeying for a bigger role in Rousseff's government and more funds for its members' districts in an election year.

"The government has neglected the allied parties and their leaders," said PMDB lawmaker Danilo Forte, who proposed calling a party convention to decide whether to end the alliance with Rousseff's leftist Workers' Party (PT).

The rebellion comes at a bad time for Rousseff as she plans to run for re-election in a scenario complicated by economic downturn and rising inflation in Latin America's largest nation.

Government and foes were surprised by the extent of Tuesday's defeat that showed the strength of the disaffected bloc in Congress. The lower house voted 267-28 to set up a special committee to monitor investigations by the Netherlands and Petrobras into the bribery case involving Dutch ship leaser SBM Offshore NV.

The allegations by the unidentified former SBM employee suggest that Petrobras officials were paid $139 million in bribes through an intermediary.

The committee has no power to subpoena witnesses and its work is not expected to lead to any consequences for the government. But it can draw attention to a bribery case that would be fodder for Rousseff's opponents on the campaign trail.

Rousseff chaired the board of Petrobras as minister in the government of her predecessor and mentor Luis Inacio Lula da Silva when the bribes were allegedly paid. A scandal could also hurt then president of Petrobras, José Sérgio Gabrielli, who is running for governor of the northern state of Bahia this year.

Political analysts say the coalition crisis is of Rousseff's own making because she dislikes backroom politics and lacks the charisma and political skills that helped Lula forge today's ruling coalition.