Mexico City  - Mexican President Felipe Calderon and his centre-right National Action Party (PAN) on Sunday face a midterm legislative election that is considered a rehearsal for the 2012 presidential contest.

"These (midterm) legislative elections in Mexico and in many parts of the world are a sort of referendum on the performance of the executive administration, that is PAN and Calderon," researcher Joy Langston, of the Centre for Economic Research and Teaching, told the German Press Agency dpa.

Amid a generalized disappointment with politics as a whole, 77.5 million Mexicans will be called upon to fill 500 seats in the lower house of the federal Congress. The election will also select six state governors, 552 mayors and 434 local legislators, in 11 of Mexico's 32 states.

Three years ago, PAN became the largest fraction in the lower house of the Mexican Congress for the first time in its history, and Calderon beat leftist Andres Manuel Lopez Obrador by a very small margin.

In that election, the leftist coalition around Lopez Obrador came second, but it is now very divided. The Revolutionary Institutional Party (PRI), which governed Mexico for 71 years before losing power to PAN in 2000, is currently the third-largest bloc.

According to opinion polls, the PRI could get a resounding win Sunday and regain its majority in the chamber, a situation that would leave it well-placed in its efforts to recover the presidency in three years, when Calderon cannot stand for re-election.

"(The election) also matters a lot for any governor who wants to be president or a presidential candidate in 2012," Langston said. "(The PRI) remains an extremely powerful party, and what everyone is waiting for is that one way or another the PRI is going to be the party that wins in 2012."

A fire at a day care centre in the state of Sonora that killed 48 children last month is likely to play a role in the election, overshadowing points the government earned for its handling of the outbreak of the swine flu, A(H1N1), epidemic in April.

The election will take place exactly a month after the fire, and Mexican society remains to a large extent in shock over the tragedy. Several children were still in hospital with serious injuries - with the lives of some still at risk. The PAN and the PRI are blaming each other for what happened, without any high officials having paid the political cost of the tragic events at the federally supervised facility.

Sonora, which is currently ruled by the PRI, will chose a governor on Sunday.

In protest, several public figures have called upon the electorate to annul their votes, in a country in which voting is compulsory for all adults.

The economy is another factor that is likely to weigh in on the voting, with a sharp fall in gross domestic product (GDP) and major job losses in recent months amid the severe global economic and financial crisis.

Mexico's electoral authorities will be closely watched, after fraud allegations marred the presidential election in which Calderon reached the presidency. (dpa)