MEXICO CITY (Reuters) - The Mexican government's pledge to tackle graft suffered a setback on Friday when Congress entered its summer recess having failed to pass anti-corruption legislation that has been stuck in political limbo for months.

Harried by accusations of corruption, President Enrique Pena Nieto's government last May passed a reform to tighten oversight of public officials, and create a special anti-graft prosecutor.

Those changes were dependent on secondary legislation meant to pass in a year, yet by the end of April, his centrist Institutional Revolutionary Party (PRI) had only submitted proposals for five of the seven laws the package comprises.

The opposition attacked Pena Nieto's commitment to the reform and blamed the PRI for blocking the legislation, which the party admits will likely miss the May 28 deadline.

"The president is from one party, and it's up to him to push this reform. And what's happening is the very opposite," said opposition senator Francisco Burquez of the center-right National Action Party.

Taking power in 1929, the PRI ruled Mexico for the next 71 years and had become a byword for corruption when it was finally voted out in 2000. Pena Nieto returned it to power in 2012.

Presidential spokesman Eduardo Sanchez dismissed any suggestion that Pena Nieto was not doing enough, saying that the legislation currently in Congress came from the president, and that his commitment to the cause was "more than proven".

PRI Senator Enrique Burgos said his party needed more time to incorporate recent civil society proposals to make officials disclose their financial interests, tax returns and assets.

"We don't want to be accused of opposing transparency or the fight against corruption, we have an interest in demonstrating the opposite," Burgos said, noting that investment and Mexico's reputation depended on taking a stand against corruption.

The legislation was unlikely to pass before June 5 state elections, but should do so in a special session "well before" Congress reconvenes officially in September, Burgos added.

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Still, Francisco Rivas, director of the National Citizen Observatory, a civil group which monitors justice and security in Mexico, said there was a clear contradiction between the government's rhetoric on graft and what the PRI had achieved.

Pena Nieto became the center of a conflict of interest probe last year after reports revealed he, his wife and his finance minister bought homes from government contractors. Pena Nieto named the head of the probe, who cleared them of wrongdoing.

(Reporting by Dave Graham; Editing by Muralikumar Anantharaman)