(Adds governors targeted by prosecutor, comment by Congressional leader, presidential aides play down protests)

By Anthony Boadle and Lisandra Paraguassu

BRASILIA, March 15 (Reuters) - Brazil's president and senior lawmakers redoubled their support for a major pension reform on Wednesday despite nationwide protests against the proposal and the expansion of a graft probe threatening the ruling coalition.

The government's agenda received a vote of confidence from Moody's Investors Service, which cited progress on fiscal reforms as a reason for revising its outlook for Brazil's sovereign credit rating to stable from negative.

Brushing aside the protests, Brazil's currency and benchmark stock index both rose around 2.0 percent on Wednesday, leading a rally in Latin American assets after the U.S. Federal Reserve signaled a gradual pace for interest rate rises.

Wednesday's developments underscored that the political momentum is still in President Michel Temer's favor as he pushes ahead with an unpopular austerity agenda that has drawn opposition into the streets but retained the support of congressional leaders.

The public backing from legislative allies was particularly important after Brazil's top public prosecutor moved on Tuesday to target dozens of senior politicians as part of a corruption probe centered on kickbacks at state oil company Petrobras.

Brazilian media reported on Tuesday that investigations have been requested into five of Temer's ministers, including his chief of staff Eliseu Padilha, as well as the speakers of both chambers of Congress and two former presidents.

Globo TV reported on Wednesday that a sixth minister was being targeted in the probe, Trade Minister Marcos Pereira, as well as the governors of five states, including Rio de Janeiro and Minas Gerais.

Pereira, an Evangelical bishop, said in a statement that his Brazilian Republican Party had received no illegal funds and he was ready to help prosecutors dismiss "this unjust conjecture."

Despite the snowballing investigation and well-organized union resistance, Thomaz Favaro, a political analyst with global consultancy Control Risks, said Temer has built a more robust coalition than his predecessor, Dilma Rousseff, who was impeached last year as the Petrobras scandal gained steam.

"The coalition behind Temer has proven to be more stable than Dilma's and will continue to be so despite corruption investigations, due to the degree of ideological affinity that unites it on business initiatives and concern for Brazil's fiscal position," he said.

Temer's most senior congressional allies are reportedly among the politicians in the sights of public prosecutor Rodrigo Janot, but those same lawmakers said on Wednesday they were pressing on with reforms.