They are oil and water, Mars and Venus, cat and dog. And they might be the hottest pair in Mexican politics this year.

The political world is abuzz with the possibility of an election year alliance between the conservative National Action Party of President Felipe Calderon and the leftist Democratic Revolution Party, whose members are so miffed over Calderon's disputed win in 2006 that they still refuse to recognize him as president.

The two parties, which clash over everything from tax policy to abortion rights, are talking seriously about joining hands in time for gubernatorial elections in July.

It would be a loveless marriage bound by a practical goal: to defeat the once-dominant Institutional Revolutionary Party, or PRI. The party was toppled from power a decade ago, but it has reemerged as the 800-pound gorilla of Mexican politics two years before a presidential election it seems well positioned to win.

The idea under discussion is for Calderon's party, known as the PAN, and the Democratic Revolution Party, or PRD, to unite behind the same gubernatorial candidate in states where the PRI has long ruled and is favored to win again. By combining forces, the thinking goes, the two parties could assemble enough votes to dislodge the PRI.

This year's main prizes are governorships in 12 of Mexico's 31 states, but the maneuvering also has much to do with the 2012 presidential vote. Capturing governors' spots from the PRI might slow its recent momentum and neutralize its expected advantage in those states in 2012, analysts say.

The first alliance took form in the northern state of Durango last week, when the parties and two smaller ones agreed to assemble a shared slate for governor, mayors and state legislators.

The parties are also thinking about joining hands in Oaxaca, Hidalgo and Puebla states -- all PRI strongholds.

Shared fear of a PRI sweep is at work. The party sailed to victory last summer, recapturing the lower house of Congress amid an economic crisis that has hobbled the PAN and infighting that severely weakened the PRD.

Of the 12 state governorships up for grabs in July, nine are already held by the PRI. Enrique Pena Nieto, the PRI governor of the state of Mexico, sits atop most polls as the current favorite for president.

The idea of a PAN-PRD alliance has been controversial, touching off a sharp debate over whether it would be good or bad for Mexico's still-evolving democracy 10 years after the PRI lost its 71-year monopoly on power.

Not surprisingly, PRI leaders have assailed the proposed alliances as "perverse" and say they will fail at the ballot box.

"Alliances between enemies that don't respect each other are contrary to nature," said Manlio Fabio Beltrones, the party's leader in the Senate.

The proposed alliances have also prompted queasiness inside the PAN and the PRD.

Former President Vicente Fox, of the PAN, scoffed at joining with the leftists, saying it "doesn't have principles." Interior Minister Fernando Gomez Mont, also of the PAN, dismissed such alliances as "political marketing" that could end up leading to fraud. (Gomez Mont later backtracked, saying alliances can work if the parties agree on a platform.)

Andres Manuel Lopez Obrador, who as the PRD candidate lost to Calderon in 2006 and refers to himself as Mexico's "legitimate president," said it made no sense to team up against the PRI since the two parties are "the same."

But some who advocate the unlikely partnership this year say it may be the only way to advance Mexico's emerging democracy, by breaking the PRI's continued dominance at the state and municipal levels in many places.

Although the presidency changed hands in 2000 when Fox won, states such as impoverished Oaxaca remain solid PRI fiefdoms. And as presidential clout has ebbed, some analysts say, that of governors has grown.

Jesus Ortega, the president of the PRD, was pragmatic. "Politics," he said, "is not a matter of hatreds and loves."

Seasonal alliances in Mexico have cropped up for the last 20 years, but they haven't produced lasting governing coalitions and distract from the task of building an electoral majority from the ground up, said Daniel Lund, an analyst and pollster in Mexico City.

"It's an easy way out," Lund said. "To build your party, to build your voter base -- that takes a lot of work."

ken.ellingwood@latimes.com