MEXICO CITY -- With most pollsters judging Mexico's presidential race too close to call, the two leading contenders entered the final weekend of campaigning with appeals to undecided voters, including would-be defectors from the candidate running a distant third.
Yesterday, the last day polls were legally allowed to be published, the country's two leading newspapers, Reforma and El Universal, reported identical survey results: 36 percent for left-wing populist Andres Manuel Lopez Obrador and 34 percent for conservative rival Felipe Calderon.
The margin of error in both polls was bigger than the two-point gap, bolstering a consensus that Lopez Obrador's surge in recent surveys has given him an edge but failed to make him the clear favorite in the July 2 election.
Roy Campos, whose final poll gave Lopez Obrador, of the Democratic Revolution Party (PRD), a three-point advantage, said the outcome may hinge on the effectiveness of the candidates' closing messages and get-out-the-vote operations.
"Don't ask us to prognosticate," Campos told a Colegio de Mexico seminar attended by six other leading pollsters. "We cannot guess what the candidates will do."
Calderon, the candidate of President Vicente V. Fox's National Action Party, used a 30-second television spot yesterday to promote his lead in five "serious polls," distinguishing them from the seven that show his leftist rival winning. A separate Calderon ad showed headlines reporting yesterday's poll results and noted that Roberto Madrazo of the Institutional Revolutionary Party trailed badly in third place. In an appeal to wavering voters of the former ruling party, known as the PRI, a voice-over in the ad said: "Calderon is the only one who can stop Lopez Obrador."
Lopez Obrador countered with his own appeal to former supporters of the PRI, which monopolized the presidency for seven decades until Fox's upset win in 2000.
Playing to the PRI's base of low-income citizens and its opposition to Fox's free-market policies, Lopez Obrador said in a TV spot: "Everyone will benefit from a change in the economic model, above all those who earn less than 9,000 pesos [about $820] a month."
In recent days, Lopez Obrador's party has won hard-fought endorsements from several labor unions traditionally aligned with the PRI. Leonel Cota, the PRD leader, urged habitual PRI supporters this week "not to waste your vote" on Madrazo.
Both leading candidates plan to mobilize their partisans at giant rallies in the coming week - Calderon tomorrow in the 110,000-seat Aztec Stadium and Lopez Obrador on Wednesday in the zocalo, Mexico City's giant downtown plaza.
Calderon's aides say he will repeat his mantra that free trade, foreign investment and tourism can create the jobs Mexico needs to prosper. Lopez Obrador will drive home the message that Mexico can advance only by first pulling tens of millions of people out of poverty, mainly through large-scale government public works projects.
As clear as that choice sounds, many voters said in interviews this week that they are put off by the attack ads that have escalated between the two campaigns since the early spring.
"I've had it with these awful, useless and ridiculous campaigns," said Nidia Lara Zamora, a 28-year-old Mexico City software engineer. "In the end, I'll vote for the least of all evils, but so far I don't know who that is."
Pollsters at yesterday's seminar said about 10 to 15 percent of Mexico's 71.5 million voters were undecided in the final surveys, taken two weeks before the election. Some pollsters said those voters were more likely to tip to Lopez Obrador, who is slightly favored by most Mexicans who identify themselves as independent of party loyalty.
Maria de las Heras, a pollster with close ties to the PRI, said about 3 million PRI supporters who have declared their intent to vote for Madrazo may be vulnerable to appeals to switch. De las Heras was the only reputable pollster who correctly predicted Fox's victory six years ago; others had him trailing PRI nominee Francisco Labastida by an average of 2.7 points in their final polls. This time de las Heras has Lopez Obrador leading by five points in a poll with a 2.2 percent margin of error - the biggest margin predicted in any survey this week.
But she and others at the seminar were cautious about Mexico's developing and inexact science of polling.
"I don't have the slightest idea who is going to win the election," said Ulises Beltran, who was Labastida's pollster in the last race. "But I have to recognize that if the election had oddmakers, they would at this moment favor Lopez Obrador."
Richard Boudreaux writes for the Los Angeles Times.