MEXICO CITY — Pollsters say many Mexicans haven’t made a final decision on whom to support in the July 1 presidential election, leaving a debate Sunday as perhaps the last chance to shake up a race so far dominated by the former ruling party.

In a get-together with foreign correspondents, four top Mexican pollsters agreed Thursday that former Gov. Enrique Peña Nieto of the Institutional Revolutionary Party, or PRI, remains solidly in front of his two main rivals.

The analysts said Sunday’s televised debate, the second and probably last with all four candidates, could place new focus on leftist Andres Manuel Lopez Obrador, who is now second in most polls and has closed the gap slightly with Peña Nieto in recent weeks.

Pollster Jorge Buendia said as many as a quarter of respondents say they have not made up their minds. But he said that even among those undecided voters, Peña Nieto still leads Lopez Obrador of the Democratic Revolution Party, or PRD, and Josefina Vazquez Mota of the ruling National Action Party, or PAN. A fourth candidate, Gabriel Quadri of the New Alliance Party, is far behind.

Most recent polls, including one published Thursday in the daily newspaper Excelsior, give Peña Nieto, of the central state of Mexico, a double-digit lead over Lopez Obrador going into the final stretch. But on Wednesday, Lopez Obrador said his campaign’s poll put him slightly ahead.

Many Mexicans are loath to hand power back to the PRI, which ruled for 70 years before being ousted at the polls in 2000. But Lopez Obrador, a former Mexico City mayor, and Vazquez Mota, once a congresswoman and Cabinet minister, appear to be splitting those votes.

The top vote-getter will win the July election, even if he or she receives less than 50% of the ballots.

This campaign has shown little overall change over months of polling. Francisco Abundis of the Parametria polling firm displayed graphs showing the PRI ahead without interruption since 2009. The only real shift in polling has been for second place, with Lopez Obrador overtaking Vazquez Mota in recent weeks.

Analysts said the race hinged more on candidate character than any single issue, though a jobs slowdown and soaring drug violence are much on voters’ minds. Television spots tend to focus more on which candidate is trustworthy than on their plans, which often are quite similar.

“This is an election less about ideas and issues than personalities,” Buendia said.

The country’s drug war violence, with more than 50,000 dead since President Felipe Calderon of PAN took office in late 2006, has also taken a toll on efforts to measure public opinion. Poll workers find it harder than before to get people to answer questions, or even to answer the door. Security is a bigger concern for pollsters: Nine workers from Parametria and the Mitofsky polling firm were briefly kidnapped last year in the western state of Michoacan.

Marcelo Ortega, general director of the Mitofsky firm, said the company has stepped up precautions, such as by having poll workers travel in cars with local license plates, rather than in vehicles from Mexico City. Ortega said, though, that polling firms were still able to do their jobs.

ken.ellingwood@latimes.com