Mexico City  - Mexico's Institutional Revolutionary Party (PRI) held power for more than seven decades in Mexico, but its 80th anniversary falls Wednesday with the party out of power, albeit with promising opinion polls.

In the wake of the 1910-20 Mexican Revolution, the winning factions resorted to violent power struggles. The PRI was founded on March 4, 1929, to institute peaceful transitions to power among the revolutionary elements.

The PRI is a member of the Socialist International, but its policies are difficult to classify.

Over the years, it became an almighty force in the country's politics, with the Mexican president pulling all the strings in public life.

The party lost the presidency for the first time only nine years ago. In 2006 congressional elections, the PRI slipped into third place in the lower Chamber of Deputies and second in the upper Senate. The party has since regained strength.

According to an opinion survey that the Mexican daily Reforma published last week, ahead of the Mexican mid-term election on July 5, the PRI appears is polling 41 per cent, compared to 29 per cent for the National Action Party (PAN) of Mexican President Felipe Calderon.

The idea of former Mexican president Plutarco Elias Calles (1924- 28) as he founded the PRI - then called the National Revolutionary Party - was to channel the rivalries among the various military leaders of the Mexican Revolution.

In government, the PRI once controlled trade unions and the media. It sponsored opposition parties so as to keep up a democratic pretence and resorted to force to repress genuine dissidents.

Under the PRI regime - which Peruvian author Mario Vargas Llosa defined as the "perfect dictatorship" - the Mexican president handpicked his successor every six years and then had his decision validated at the polls.

In 1987, the PRI suffered the worst rift in its history. Cuauhtemoc Cardenas and a group of top-level politicians left the party, mounting a challenge at the polls. In an election that was clouded by allegations of fraud, PRI candidate Carlos Salinas still won.

Ten years later, the PRI lost - for the first time - its absolute majority in Congress. In 2000, conservative candidate Vicente Fox of the Christian-democratic PAN took over the presidency.

The electoral defeat led to a shock, and many predicted that internal divisions would shatter the PRI, once removed from the levers of power.

However, the party stuck together, at least formally, and in 2006 it became a crucial force in Congress, even without a majority. The PAN government needs PRI votes to pass any legislation.

With the PAN worn down by the exercise of power, with the ongoing international economic and financial crisis and with the wave of violence that is plaguing Mexico, the PRI hopes to do rebound in legislative, gubernatorial and mayoral elections in July.

The recovery that opinion polls show "has to do with a change of mentality, of approach, a change in the way politics is done," said the PRI's second-in-command, Secretary-General Jesus Murillo Karam.

"We are a party that has behaved with incredible seriousness in the opposition, that is making propositions, that raises issues and that is also able to seek agreements and to negotiate," Murillo Karam said.

However, some analysts think that the PRI has not changed at all, and that if it wins the election, it will be only because voters are disappointed with others.

"The PRI is the same. It simply stayed in the opposition without breaking up and, by default, people are returning to it because they see no progress and no contributions from other parties," said political scientist Jose Antonio Crespo.

In any case, 80th anniversary celebrations will be marked by the PRI's hope to regain a legislative majority and to brace its position in the country's states. From then on, its leaders insist, it will be just one step away from a return to the presidency in 2012, to restore the party to the position of power that it was designed to hold. (dpa)