Hugo Chavez, Venezuela's president, has become a regional standard bearer for anti-US movements because of his vocal criticism of the right-wing Bush regime.
The sixth world forum, an event that began in Porto Alegre in Brazil, has registered more than 67,000 participants and starts on Tuesday with a march against imperialism and war that will probably focus on George Bush, the US president, and his war in Iraq.
Lucy Martinez, a Colombian who belongs to a solidarity group with Cuba, said: "This is a process that can bring change for everyone. It's great that it is here in Venezuela because Chavez, like Fidel Castro [the Cuban president], is an example for everyone."
Ecuadorean Indians in traditional shawls sat among piles of luggage while Brazilian students checked out street stalls offering Che Guevara T-shirts and bracelets, watches and posters printed with Chavez's image.
Lines of participants waiting to register snaked inside the Teresa Carreno Theatre complex and officials set up a campsite in a public park.
Many travelled by road from neighbouring Brazil and Colombia.
Morales (L) shares Chavez's (R)
The forum began as an alternative to the gathering of world leaders in Davos, Switzerland, but it is now a broad movement where activists campaign for everything from fair trade and gay rights to debt forgiveness and anti-globalisation.
Two parallel events have been organised in Mali and Pakistan.
The forum took place as Evo Morales, Bolivia's new president, became the latest popular reformist leader to assume power in South America on a wave of regional rejection of US-backed free-market economic policies.
The event bills itself as independent. But much attention is likely to focus on Chavez, a former soldier who has branded Bush "Mr Danger" and whose aim is to use his socialist policies to better the lives of the poor in his oil-rich country.
Benjamin Inuca, president of an Ecuadorean indigenous association taking part in the forum, said: "With Chavez taking some incentives for the poor we wanted to know more."
The forum in Caracas has attracted
more than 67,000 participants
Chavez, who often claims inspiration from Simon Bolivar, a South American liberation hero, says he has sought out trade and energy deals with South American neighbours to counter Washington's damaging influence in the region.
US officials dismiss Chavez's accusations that they are plotting his overthrow.
The World Social Forum's website is at: http://www.forumsocialmundial.org.br/