Francisco Labastida Ochoa rode to victory in Mexico's first presidential primary on the seemingly immutable attitude of voters like Benjamin Levin, a 29-year-old Mexico City computer specialist.

"We came out to vote so that the country can continue with more of the same instead of making a mistake with something new," Levin declared.

And Labastida, crowned as the nominee of the long-ruling Institutional Revolutionary Party (PRI), will be hard to stop in the presidential election in July because of voters like Aurora Garcia, 64, who works cleaning downtown offices.

"My mother taught us that we should vote for the PRI and I always have," she said. "It is our obligation as Mexicans."

Thus armed, Labastida will face two main contenders in July: former Guanajuato state governor Vicente Fox of the center-right National Action Party and former Mexico City Mayor Cuauhtemoc Cardenas of the leftist Democratic Revolutionary Party. Labastida was in a dead heat with Fox in a countrywide survey last week by El Universal newspaper, each with about 42 percent. Cardenas polled about 13 percent.

Labastida, a former state governor and cabinet minister who has been a PRI loyalist his entire career, is widely seen as the favorite of President Ernesto Zedillo and the party establishment, and he owes his primary victory in large part to the power of a political machine that has not failed its candidate in 70 years of uninterrupted rule.

He trounced a self-styled PRI rebel, Roberto Madrazo, a former governor who waged an unusually aggressive and negative campaign. With 82 percent of Sunday's primary votes counted, Labastida had won 272 of 300 electoral districts compared to wins in a meager 20 districts for Madrazo.

Political analysts and observers also blamed Madrazo's thrashing on a campaign crippled by strategic errors and one that badly miscalculated the impact of relentless attack advertisements on an electorate witnessing its first political campaign dominated by the electronic media.

"People are more cautious and conservative than Madrazo and observers have been thinking," said Federico Estevez, a former assistant to Zedillo now on the faculty of the Center for U.S.-Mexican Studies at the University of California at San Diego. "He was betting on there being a greater discontent within the PRI, a greater desire for rank-and-file-generated change."

Given the size of Labastida's victory, it appeared unlikely that there would be a split in the PRI, which emerged from the campaign looking strong and united. Opposition parties had hoped a disgruntled primary candidate--notably Madrazo--would bolt, damaging the PRI's prospects in next year's presidential election.

While all three losers acknowledged defeat, however, none immediately endorsed the results or offered congratulations to Labastida. They apparently withheld support in the hope that Labastida will offer them a consolation prize such as a seat in Congress or an ambassadorship.

Madrazo's bargaining power has been significantly weakened, however, by the scope of his loss and the strong performance of the PRI vote machine, which holds out the promise of a victory for Labastida in July.

"He's pragmatic, he knows that his only chance of survival is within the party," said Joel Estudillo, a political analyst at the Mexican Institute of Political Studies. "Rebelling against the PRI only works if you're inside the party, because most people who leave never get off the ground."

Madrazo began the campaign season with advertisements that built an image of himself as a friend of the poor and disenfranchised. But he quickly turned to attack ads--blasting Labastida as the "official candidate," a liar and failure--and never paused to explain who he was and what he could accomplish.

"In his first spots, he differentiated himself, but he needed to talk about the issues, and the only issue he had was that he was not Labastida," a Mexico City political consultant said.

Stanley Greenberg, U.S. polling adviser to the Labastida campaign, said surveys in September showed voters tiring of the attacks. When polls spotted the trend, Labastida's team moved toward ads that would boost confidence in the candidate as a person, focusing on honesty, strength of character, beliefs and empathy for common people, campaign officials said.

A survey last week by the daily newspaper Reforma showed that, with 57 percent of the people consulted, Madrazo succeeded in defining Labastida as the "official candidate" of the PRI--the one anointed by the president and backed by the party machine. The poll also found that respondents viewed Labastida as the most honest, the most sincere and the most likable of the four primary candidates.

"Zedillo kept his word and stayed out of the race," a top Labastida strategist said. "But Madrazo said Labastida was the official candidate, and that helped. PRI-istas [party members] said, 'Thank you very much. Now I know whom to support.' "

CAPTION: Based on 82 percent of the vote, Roberto Madrazo won just 20 of 300 electoral districts in the primary.