Among the cheering thousands in Santiago's Constitution Plaza, Guillermo Vega wore a smile with more voltage than the spotlights shining down on the country's new president, Ricardo Lagos.

Lagos, a celebrated former dissident, had just been elected the first Socialist president since Gen. Augusto Pinochet's bloody coup ousted Salvador Allende 27 years ago in the very same square. And Vega, a 19-year-old Santiago law student who came to hear the Sunday evening victory speech, raised his hands in the air and shouted for joy as he took in Lagos's promise of economic justice, respect for human rights and deeper democracy.

These are promises that millions of Latin Americans have heard before--generally only to see them broken. Vega is nevertheless among those riding a wave of optimism surrounding Lagos that is washing over Chile and beyond. "Today, I feel like I have a future," said Vega, the son of an unemployed store clerk whose family has had a hard time coping with a grinding recession in Chile. "I have hope, you know, that this guy really means it. I'm counting on him."

And so are a lot of others. Lagos, a 61-year old economist educated at Duke University, has become the champion of a new, left-leaning message for Latin America. It says it is possible to fight the region's gravest problem--gross income disparities between the wealthy and the vast underclasses--without violence and within the confines of the free markets and parliamentary democracies established over the last two decades.

As Latin America struggles through yet another period of economic and political upheaval, especially in such nations as Ecuador, Venezuela and Colombia, Lagos has been invested with the hopes of many who embrace his search for that Latin American third way--avoiding the revolutions and dictatorships of the past but fighting the economic disparities of the present.

"The expectations are that he will build a model in the region through his attempt to change Chile into a just, social democracy," said Marta Lagos, a Santiago-based political analyst, who is not related to president-elect. "He is a light of democracy in Latin America at a time when many Latin Americans have lost faith in democracy as a tool to better their lives."

Sensing widespread frustrations with the disparities left by market-oriented economic reform, Lagos's right-wing rival, Joaquin Lavin, also embraced the themes of inequality and poverty-busting, making inroads in Indian and other poor communities that typically support the left. Lavin's success--he lost Sunday's vote by only 3 percentage points--came largely by shifting the conservative agenda toward the political center and emulating Lagos with a message of change that seems to resonate across the continent.

In Latin America today, all countries except President Fidel Castro's Cuba are free of military rule. But polls show that only two nations, Uruguay and Costa Rica, indicate a rate of satisfaction with democracy of over 50 percent. Although massive government corruption has promoted much disillusionment, analysts say it also stems from the fact that the benefits of the new free market have gone disproportionately into the hands of the rich.

Enter Ricardo Lagos. In March, when Lagos moves into the presidential palace once occupied by his old foe, Pinochet, Chile will become a closely watched Latin American laboratory for Lagos's European-style socialism, which bears no resemblance to the divisive Marxist policies advocated by Allende.

In the very nation that became the model for free market reform in the 1990s, his moderate leftist platform calls for the state to play a greater role in offering a range of new social services, such as unemployment benefits and oversight of privatized utilities that today, as in much of Latin America, operate largely without government regulation.

"We want to be the star country of the new millennium," said Lagos, "overcoming inequality and offering the same opportunities to all of our children."

Disenchantment with weak and corrupt political institutions has fostered the rise of elected presidents with authoritarian tendencies, such as Peru's Alberto Fujimori and Venezuela's Hugo Chavez. But Lagos, along with Argentina's new President, Fernando de la Rua, and Brazil's Fernando Henrique Cardoso, hopes to define a new school of Latin leadership, in which corruption and inequalities are not tolerated and, at the same time, democratic institutions and civil liberties are strengthened.

Lagos brings to the table a history of fighting for democracy unlike that of any other leader in the region. An exile during Pinochet's rule in the 1970s, he came back to Chile in the '80s to confront the feared dictator. On national television during a referendum campaign that would ultimately force Pinochet from power in 1990, Lagos emboldened the nation by wagging his finger at Pinochet and warning him that he must be called to account for the atrocities of his government.

"Chile is marking the end of an era that was filled with difficulties and pains and launching a new one, where freedom of expression, civil liberties and economic equality are all going to dominate government," said Sen. Sergio Bitar, another Pinochet opponent.

Democracy in Chile is still tainted by a constitution drafted during the Pinochet era that provides for a number of appointed senators--largely from the far right and allied with the old military dictatorship. Lagos has promised to make eliminating those posts one of his top priorities.

But perhaps his biggest challenge remains the unfinished business with Pinochet--who has been under house arrest in London for 15 months fighting an extradition request from Spain on human rights charges but may soon be returned to Chile because of ill health. As Lagos delivered his speech Sunday night, he was interrupted by the chanting crowd, which screamed: "A trial for Pinochet! A trial for Pinochet!" Although Lagos was trying to start his term on a note of political unity, he stopped speaking, looked at the crowd and answered: "The Chilean courts will do their job, and I am going to make sure those courts are respected!"

But analysts here say Lagos will have to do a lot more to win the respect of the people who voted for him.

And in a nation with a wealthy establishment whose candidate gave Lagos a hard run for the presidency, he not only will have to push through his economic theories but make them work as well.

"In Lagos, we may have a chance for justice, but he's got to prove it," said Congressman Juan Pablo Letelier, son of Orlando Letelier, a Chilean ambassador to Washington who was assassinated there in 1976 by Pinochet's secret police.

CAPTION: Lagos salutes his supporters as he arrives to vote in Sunday's election.

CAPTION: Exultant Chileans reach out to president-elect Lagos as he visits a Santiago drug rehabilitation center a day after his victory at the polls.