(Adds party decides no member can join cabinet, Temer re-elected)
By Anthony Boadle
BRASILIA, March 12 (Reuters) - Brazilian President Dilma Rousseff's main coalition partner served notice on Saturday that it could break from her embattled Workers' Party government in 30 days and join opposition efforts to unseat the leftist leader.
At a rowdy convention of the fractious Brazilian Democratic Movement Party (PMDB), leaders quashed a motion by irate delegates who wanted to quit Rousseff's government immediately, before it goes down in a political storm over corruption and economic recession.
Instead, Brazil's largest party agreed to put off that decision for 30 days and leave it to the party executive committee, ensuring unity behind its leader, Michel Temer, who is Rousseff's vice president.
Party insiders said this gives the PMDB time to gauge the level of support in the country for the impeachment of Rousseff sought by opposition parties in Congress, which could put Temer in the presidential seat. Rousseff's opponents have called nationwide demonstrations against her on Sunday.
While the PMDB has six ministers in Rousseff's cabinet, the convention banned members from accepting new posts until the party decides to leave the government or not in one month.
The widening corruption probe surrounding state-run oil company Petrobras has turned many PMDB lawmakers against Rousseff, threatening to split her coalition and increasing chances of her impeachment in Congress this year.
Plea bargain testimony by defendants in the bribery and political kickback scandal have led prosecutors closer to Rousseff's inner circle, including Workers' Party founder and former president Luiz Inacio Lula da Silva who is being investigated for allegedly benefiting from graft money.
The anti-Rousseff faction of the PMDB rallied the convention with chants of "Out with Dilma" and "Out with the Workers' Party" and "Temer for president."
"This was the PMDB's most anti-Workers' Party convention in 12 years. Not a single leader spoke in favor of the government, even the ministers in the cabinet remained silent," said Darcisio Perondi, a lawmaker from Rio Grande do Sul state.
The PMDB reconfirmed Temer as its leader by 96 percent of the votes cast, a sign of unity in a party that is touting itself as the best option to overcome Brazil's political crisis and pull the country out of a severe recession.
In his speech, Temer said the PMDB has a blueprint to stimulate business, reduce the size of government, create new jobs and restore growth to an economy that shrank 3.8 percent last year, its worst performance in 25 years.
PMDB party members are increasingly impatient to distance themselves from the unpopular Rousseff and her ruling Workers' Party that has been in office since 2003.
"This government will fall, it cannot survive. Either we abandon ship now or go down with it," said Carlos Marun, a lawmaker from the farm state Mato Grosso do Sul.
If Rousseff is not impeached, Marun warned, Brazil's top electoral court could annul the Rousseff-Temer election win in 2014 in an investigation of graft money allegedly used to fund their campaign.
Several of the PMDB leaders standing next to Temer at the convention are themselves the target of corruption probes, including the speaker of the lower house of Congress, Eduardo Cunha, who has been indicted for laundering money in the Petrobras kickback scandal.
The PMDB, a party with no fixed ideology, has been in power ever since Brazil restored democracy in 1985 after two decades of military rule, either in the government or controlling one of the two house of Congress.
The PMDB plans to field it own presidential candidate in the next elections in 2018, but if it decides to break with Rousseff sooner rather than later as many of its members now want, her impeachment is all but certain and Temer would finish her term. (Reporting by Anthony Boadle and Lisandra Paraguassú; Editing by Mary Milliken)