SAN MIGUEL, Argentina—As a “point man” for the ruling Peronist movement, Javier Llanos works teeming slums of dirt streets and plywood homes, exhorting prospective voters in this industrial suburb of the capital to cast ballots for Daniel Scioli in Sunday’s presidential election.
But the working-class districts that ring Buenos Aires—packed with millions of voters who powered Peronism for decades—are slipping from the movement’s grasp.
Six polls show that opposition candidate Mauricio Macri, the business friendly mayor of Buenos Aires, has a lead of five to 13 percentage points over Mr. Scioli, a signal that after 12 years, a movement that thrives on a mix of welfare programs and nationalism may be defeated.
“We’ll lose it all if Macri wins,” lamented Mr. Llanos, echoing the Peronist message that a vote for change will mean disaster for Argentina. “There will be a lot of suffering for the poor.”
But many Argentines—even those in poor districts who benefited from years of generous programs—disagree. They speak of decaying or nonexistent infrastructure and rising crime and drug trafficking under Mr. Scioli, who has been governor of the Buenos Aires province for the past eight years.
“I’m 52, and I have always known Peronism,” said voter Susana Arraskaita. “I want to see something different.”
Mr. Scioli, a 58-year-old former powerboat racing champion, fell short of the threshold needed to win in a first round of voting on Oct. 25 and barely squeaked by Mr. Macri, 56. Other outcomes of that election also went against President Cristina Kirchner and the Victory Front, the Peronist coalition she leads.
In large and populous Buenos Aires province, Mrs. Kirchner’s choice for governor, her mercurial cabinet chief Aníbal Fernández, lost in the October vote to Mr. Macri’s young and charismatic candidate, María Eugenia Vidal—the first time in 28 years a non-Peronist won that post.
The Victory Front’s mayoral candidates also took a beating in the 33 densely populated districts that ring Argentina’s capital and contain about 27% of the country’s 32 million voters, with Mr. Macri’s allies scoring victories in Peronist strongholds like the bedroom city of Lanús, population 500,000.
“With the results, the myths collapsed,” said Damián Sala, an activist who works for Lanús Mayor-elect Nestor Grindetti. “We learned that even in Lanús, a movement that’s not Peronism could win.”
Peronists are now feverishly trying to get the votes they need—a campaign to be won or lost in these 33 key districts. Of particular interest to both sides are three million votes that a dissident Peronist, Sergio Massa, received in the first round.
“The mother of all battles takes place in these working-class suburbs,” said Carlos Coronel, a teacher whose second job as a local Peronist representative entails organizing activists to convince San Miguel’s voters to cast ballots for Mr. Scioli.
In Mrs. Kirchner’s two terms—and in her husband Néstor’s previous 2003-07 term—Peronism has meant largess here in the capital’s industrial belt.
In the most costly expansion of social welfare since the rule of Peronism’s founder, Gen. Juan Domingo Perón, more than six decades ago, it has delivered everything from pensions for retired manual laborers to stipends for young mothers. For those fanatical about soccer, there is “Football For All,” which broadcasts games free that had once been available only on pay-per-view. Those who are hard to employ can work in government-supported neighborhood cooperatives, producing T-shirts or toys.
Peronist organizers now remind people here that deprivation and economic calamities of the past—like the 2001 debt default, which led to riots and poverty—took place under non-Peronist leaders.
“I remember 2001, I lost everything,” said Pedro Multari, a 54-year-old San Miguel resident. “We had to start selling things so we could have enough to eat.”
Peronism built up a fierce loyalty decades ago, winning territorial control by forging close ties to organized labor, said Rodrigo Zarazaga, a Jesuit priest who has spent two decades as chaplain in these downtrodden communities. Under the Kirchners, allegiance has been secured with public assistance.
But it has come at a cost. Ballooning government spending has fueled inflation, the second-highest in Latin America, which hits the poor hard. Rev. Zarazaga said the state has also ignored infrastructure: Nearly half of all households are without sewerage or potable water in the cities ringing Buenos Aires. Many roads are unpaved, large urban areas are prone to flooding,schools are decaying and decrepit commuter trains are overcrowded.
“The urgency was to resolve problems with massive cash transfers, but the lack of infrastructure is a problem,” said Rev. Zarazaga, a Harvard-trained social scientist who directs the Research and Social Action Center, a Buenos Aires think tank. “If Mr. Scioli doesn’t recover lost ground in these suburbs, he doesn’t have a chance.”
Mr. Macri’s efforts to win support in working-class wards haven’t been easy. The message activists of his Let’s Change coalition have hammered home in small-scale meetings with voters is that for Argentina to have a stable economy, it must resolve such issues as falling reserves and the lack of access to credit, said Lanús Mayor-elect Grindetti, who is currently Mr. Macri’s finance chief in the capital.
“That’s not the first problem people think about,” Mr. Grindetti said.
A few miles to the northwest, Mr. Coronel, the Peronist organizer in San Miguel, acknowledges how hard it has been to rev up the base. “There’s a sense of fatigue with regards to Mrs. Kirchner, so the runoff looks complicated,” he said while driving in San Miguel’s neighborhoods.
Mr. Coronel and other Peronist organizers have been actively trying to help residents with everyday problems, from assisting senior citizens with paperwork for pension benefits to sprucing up sport facilities. The idea, they say, is to make clear that their help is tied to Mr. Scioli.
“What some call populism is pejorative for us,” Mr. Coronel added. “We see this as social justice.”
Even with the headwinds for Peronism, many remain loyal.
In a San Miguel avenue where Peronist activists pass out pro-Scioli pamphlets, 63-year-old María Cristina Miranda recounted how she received retirement benefits under Mrs. Kirchner´s administration, though neither she nor her employer had ever contributed to a pension plan. And she doesn’t want to lose it.
“I pray to God and the Virgin that Scioli will win,” she said.