SAO PAULO, Brazil (AP) -- Former union boss Luiz Inacio Lula da Silva won Brazil's presidential election runoff by a landslide Sunday, marking a historic shift to the left for Latin America's largest country.
Ruling party candidate Jose Serra conceded defeat, shortly after Silva's Workers Party had declared their candidate the winner.
"I think Brazil can play an extraordinary role in this American continent, so that we can build an effective world peace, where countries can grow economically and socially for the well-being of their people," Silva said in his victory speech, as thousands of his supporters celebrated in the streets.
A somber Serra, a former health minister backed by the outgoing government, wished Silva "good luck in leading the destiny of Brazil."
"The voters have decided that Brazil during the next four years will be governed by my rival," Serra told supporters at his campaign headquarters.
With 97 percent of the vote counted, Silva -- a former shoeshine boy who rose to become the head of a labor union -- had 61.5 percent and government-backed candidate Jose Serra had 38.5 percent, the government Supreme Electoral Tribunal announced.
Thousands of Silva supporters gathered in the streets of Sao Paulo and Rio de Janeiro, waving his party's red flag in celebration.
"This is our opportunity to consolidate our hopes for a Brazil which should be more just, and care more about the needs of the people," said Marcos Xavier, a university professor who stood amid some 1,000 Silva supporters on Sao Paulo's main avenue.
While the votes were still being counted, the White House offered its congratulations to the winner.
"The president congratulates the winner of the election and looks forward to working productively with Brazil," said press secretary Ari Fleischer, speaking to reporters aboard Air Force One, while returning from an economic summit in Mexico.
Silva's criticism of free-market policies is at odds with Washington. His election could complicate President Bush's goal of creating a hemispheric free-trade zone by 2005. But the administration has been careful not to criticize Silva during the campaign, aware that any comment could be seen as interference.
Silva, popularly known as "Lula," just missed a victory in the first-round election on Oct. 6, forcing a runoff against Serra, a former health minister with the ruling party.
Silva's election marks a historic shift to the left for Brazil, which has never elected a leftist president. Its last leftist leader was Joao Goulart, a vice president who assumed power in 1961 when the centrist president resigned. Goulart served 2 1/2 years before being deposed by a right-wing military coup.
Brazilians are caught between hopes that Silva will reverse rising unemployment and economic stagnation and fears that the former radical union leader could worsen the country's economic woes.
"Lula is the only who can bring about the changes that the country needs to reduce unemployment and improve the standard of living of the people," said Eloisa Marques, 38, laid off earlier this year from a drug store.
But standing next to Marques in a voting line in an industrial suburb of Sao Paulo, Waldir Conde said he preferred Serra.
"Lula doesn't have experience to govern," Conde said. "To rule a country like ours, which is dominated by the United States, it is necessary to have a lot of experience and a firm hand. Serra showed he has that."
Brazil's next president will have to pull the world's ninth-biggest economy from the brink of recession, create more jobs and try to lift nearly 50 million Brazilians from poverty.
As he voted in a school in a working class neighborhood of Sao Paulo, Silva spoke of those Brazilians, and the millions of others who live a hand-to-mouth existence.
"I want to dedicate this election to the suffering poor of our beloved Brazil," Silva said as some 200 supporters outside waved Brazilian flags and small plastic banners with the slogan "Now it is Lula."
Silva hoped to celebrate his 57th birthday, which fell on election day, with a victory, capping his rise from the son of a poor farmer to leader of Latin America's biggest and most populous nation.
He left school after the fifth grade to sell peanuts and shine shoes on the outskirts of Sao Paulo. At 14, he began working in a factory, where he lost his left pinkie finger in a machine press.
In a Sao Paulo slum, or favela, pro-Silva sentiment was prevalent.
"He was the only one -- as a metalworker union leader -- who helped the poor," said Nelson Luiz da Silva Pelotti, a 56-year-old retired metalworker.
But even in an area that is a base of support for Silva, his radical past haunted him.
"I don't like communists in my country," said Silvio Alvano, a taxi driver who lives in the slum, adding that he was voting for Serra.
Silva first ran for president in 1989 as the candidate of the Workers Party, urging landless farm workers to invade private property and calling for a default on Brazil's foreign debt, which now stands at $230 billion.
However, in the three subsequent presidential campaigns, Silva moderated his radical tone.
Silva has criticized current President Fernando Henrique Cardoso's unbridled free-market policies but is believed to be considering several fiscal conservatives as members of his economic team.
Cardoso -- who privatized many of Brazil's giant monopolies and lowered import taxes, but failed to help millions of poor Brazilians -- has led Brazil for two four-year terms. He was barred from seeking a third.