By Dave Graham
MEXICO CITY (Reuters) - Reeling from their worst electoral drubbing in a generation, Mexico's main opposition parties are poised to join forces in state elections to weaken President Enrique Pena Nieto's ruling party before the next presidential election.
The center-right National Action Party (PAN) and leftist Party of the Democratic Revolution (PRD) had their worst showing since 1991 in June legislative elections and are anxious to turn the tide in a record 12 races for state governor next year.
Nine of the states are run by the ruling Institutional Revolutionary Party (PRI), and the PAN and PRD are likely to join forces in at least some of those.
They hope to capitalize on discontent over gang violence, weak economic growth and home purchases by the president, his wife and his finance minister from government contractors that have raised conflict-of-interest accusations.
Success against the PRI in those races would put Pena Nieto on the back foot and strengthen the opposition parties' chances ahead of the next presidential contest in 2018.
Nearly all of a dozen well placed PAN and PRD lawmakers consulted by Reuters said they expected the two to form tie-ups in 2016, even including some who oppose the strategy. None took the opposite view.
"What the opposition must do is unite," said Guadalupe Acosta Naranjo, a former PRD chairman and its new deputy leader in the lower house of Congress, which started a three-year term on Tuesday.
The PAN and PRD have joined forces in the past to challenge the PRI in state elections, notably in 2010.
This time, instead of coalescing around disgruntled former PRI politicians, they aim to restore their battered fortunes by recruiting unaffiliated candidates and backing independents.
The June elections strengthened the PRI in the lower house, adding a few seats to the slim majority it and its allies hold. It also controls nearly two-thirds of Mexico's 31 states.
But the party is vulnerable, and Pena Nieto's ongoing woes have dragged his approval rating to multi-year lows for a Mexican president.
The opposition's credibility has also been hit by scandals. PAN officials were accused of taking kickbacks and local PRD officials were apparently involved in the massacre of 43 students by a drug gang in league with a corrupt city government in the state of Guerrero last year.
Fernando Belaunzaran, a departing PRD congressman seeking to lead his party, says the PRD and the PAN need to find strong, external candidates that can unite them against the PRI.
"The worst thing we can do is leave the road open to the PRI," he said. "If we want to put up a real fight in 2018, the right thing to do is to take away their bastions."
Talks between the two parties to explore coalitions have already been held, he said.
But how far they go is unlikely to be clear until the PRD leadership race ends this autumn. The PAN is likely to go it alone in some states.
The PAN has been dogged by infighting since losing power in 2012, but worst hit has been the PRD, whose former leader Andres Manuel Lopez Obrador created a schism in the left by founding a new party after finishing second to Pena Nieto three years ago.
"If the left doesn't unite, we're going to have to seek alliances with the PAN against the PRI," said the PRD's Acosta Naranjo.
The PRD sees reconciliation with Lopez Obrador as unlikely, certainly by next year, making tie-ups with the PAN almost inevitable.
"We're not closed to any alliance," said Marcelo Torres, the outgoing lower house leader of the PAN. "We have to make traditional politicians understand that Mexico has changed."
A trio of PAN-PRD state election wins in 2010 were fronted by former PRI officials, and many opposition lawmakers dismiss the model as a failure. Independent, "citizen" candidates offer a viable alternative for both PAN and PRD, said Torres.
Some in the PRD in particular - which won just 11 percent of the vote in the June elections, barely half the PAN's tally - are wary of aligning themselves with their rival.
Zoe Robledo, a PRD senator also running for the party leadership, said the PRI's greatest fear was facing a united left. Coalitions with the PAN would undermine this and risked turning his party into a "satellite" of the other, he said.
But even Robledo, who, like Belaunzaran, wants half the PRD's candidacies to be open to non-party members, said PAN-PRD coalitions next year were the "most likely" outcome.
"It'll be very hard for the PAN to be successful by itself," said Juan Carlos Romero Hicks, a PAN senator and former governor of Guanajuato state. "And for the PRD too, because alone, it's very weak."
(Reporting by Dave Graham; Editing by Kieran Murray)