Another world isn't just possible - it looks rather like this. Dozens of food co-operatives surround a sea of tables and a cacophony of debate in every language under the sun. We have just escaped from the sweltering Gigantinho ('Little Giant') indoor stadium, where we sang a gentle lament for Ché Guevara and broke into chants of 'Don't Attack Iraq!' amid a forest of Palestinian flags. Never a fan of the mass meeting, I've been stirred all the same.

This is the third World Social Forum in Porto Alegre, southern Brazil. At the first Forum here, just two years ago, few could have imagined that 100,000 people from all over the world would turn up in January 2003. Farmers, trade unionists, environmentalists, artists, academics, activists, men, women, children, black, brown, white, green, red, pink, plain folk of all kinds give seminars, stage shows or mount impromptu demonstrations in miraculous harmony. Cosmopolitan tribes of young people will probably remember this for the rest of their lives. Even the gnarled gurus of abstraction are carried away by it all and start discussing 'Life After Capitalism'. No-one rules, everyone contributes - and it works.

A rare scent of epiphany, of realistic hope, is in the Latin American air. The immediate source of it is obvious - 'progressive' regimes are being elected all over the continent. 'Lula' da Silva, inaugurated a few weeks earlier as the first working-class President of Brazil (see article), has also come to the Forum in Porto Alegre, a city run for more than a decade - and to visibly good effect - by his Workers' Party. Hugo Chávez, whose 'Bolivarian Revolution' in favour of the poor is making waves in Venezuela (see article), has been here as well. Evo Morales, the leader of the cocaleros (coca growers) who nearly won the last presidential elections in neighbouring Bolivia, would have been here had events back home not taken a turn for the worse (see article). In Uruguay, a short distance to the south of Porto Alegre, the Frente Amplio ('Broad Front') of left-wing parties expects to win presidential elections in 2005 (see article). In Ecuador, newly elected Lucio Gutiérrez owes his presidency to a movement created by indigenous peoples (see article). No-one in Argentina knows quite what will happen next - but some say the country has never been more nearly in the hands of its own people (see article).

Photos: Ian Nixon

There has not been a moment quite like this in Latin America since independence from Spain and Portugal in the early 19th century. A narrow window of opportunity has opened for the majority to take control of their own continent at last. After the shameful years of military dictatorship - which began here in Brazil in 1964 and still cast a long shadow - the armed forces languish in disrepute. Washington DC, which sponsored so much of the repression, is temporarily distracted by events elsewhere. Never before has Brazil, the giant of the continent, been so prominently in the vanguard.

So why - aside from the poignancy of the fleeting moment - should I feel so apprehensive?

Perhaps it's because that scent of epiphany recalls for me the time when I lived in Chile in the early days of the Popular Unity Government, before 1973. This coming 11 September - a date now marked by another kind of terrorism - it will be 30 years since the jackboots of General Pinochet and Henry Kissinger stamped on the people of Chile. Why should not the same thing happen again? It may have started already, with a concerted effort to destroy the elected Government of Hugo Chávez in Venezuela. It is certainly well under way in Colombia.

Or perhaps I'm anxious because of the sheer scale of the task. All the new regimes in Latin America came to power by denouncing the global orthodoxy known here as 'neoliberalism'. Its prescription of free-market fundamentalism, enforced by foreign debt, has failed: the debts simply get bigger, the remedies more draconian. Yet, when faced with the 'realities' of running a government, most of the new regimes have hurried to Washington DC and shaken the appropriate hands - as the pages that follow reveal. Who needs a jackboot when a velvet glove will do? What chance can Latin Americans possibly have of overthrowing a global orthodoxy?

Well, orthodoxy is by definition an idea that has run out of ideas. Most Latin Americans stopped believing in neoliberalism long ago - if they ever did. More to the point, they have started believing in themselves. Stray just a short distance from the enclaves of wealth and you will find that the 'ideas' of Coca-Cola or the International Monetary Fund have no currency at all. You are much more likely to hear an assault on 'egotism' or to see the 'horizontalism' advocated by the Zapatistas in Chiapas, Mexico, at work. Hard lessons have been painfully learned: 'independence' is not the same thing as liberation, nor winning an election the same thing as taking control. The electoral success of Lula and the others is a sign of the epiphany, not the epiphany itself.

Which is why all those political celebrities came to the World Social Forum in Porto Alegre, where some of the ordinary folk who got them elected are gathered. These people have, among other things, developed two closely related objectives. The first is to make a clear break with neoliberal orthodoxy in its most virulent forms: the dictatorship of debt and the proposed business-friendly, US-dominated Free Trade Area of the Americas (FTAA).

The second is essential to the first. Individually, the countries of Latin America will never be able to resist the International Monetary Fund, the World Bank, the World Trade Organization, the US Government or a prospective FTAA. Working together they would be strengthened immeasurably, as the social movements of Latin America already are. It's now up to their governments to follow suit. At the very least, a better deal could then be cut with the high priests of neoliberalism. At best, the odious dictatorship of debt will be overthrown and sensible agreements made for fair rather than 'free' trade between the people of Latin America.

Which brings us back to Porto Alegre. For the time being, as the world tries to cope with the consequences of unrestrained US military power, many people in the majority world are looking to Latin America for inspiration. But the World Social Forum is just the tip of an entirely new global movement. For all its diversity, this movement faces everywhere the same orthodoxy as in Latin America. Eventually, and before too long, liberation here will hinge upon what happens in the rest of the world as well. And everyone in Porto Alegre surely knows it.