Organisers of the six-day forum which opens on Friday said the annual get-together would provide a common ground for diverse movements that led protests against last year's invasion of Iraq.
"Bush has to be stopped. His country's policies are creating devastation around the world, militarily and economically," said Chico Whitaker, who spearheaded the forum which was held between 2001 and 2003 in his native Brazil.
"We had rallied against him last year before the war and we will oppose him at the forum this year also," Whitaker told reporters.
More than 78,000 people have registered to attend the forum, but thousands more were coming in and the total attendance could top 100,000, said Nandita Shah, an Indian feminist on the organising committee for the forum.
She said the forum cost $2.4 million and that organisers were running a deficit, although she did not specify by how much.
Ford funding rejected
Organisers declined funding from the Ford Foundation, which provided about half of the money to hold the 2003 forum in Porto Alegre, Brazil.
The WSF is hoping to expand into
But Shah said the forum still received more than 25%of its funding from individual Americans or US-based activist groups.
"A lot of people in the US are interested in what is happening in the country. The US itself saw the largest demonstrations against the war" in Iraq, Shah said.
The anti-Bush tone already permeated the forum, with banners reading "Stop the USA" and "Kill Bush the Enemy" set up throughout the venue off a highway in industrial northern Bombay.
Stern-faced Indian labour organisers, Western university students with dyed hair and backpacks, and shaven Tibetan nuns mingled on the wooden exhibition grounds, swapping news about the upcoming sessions and the practicalities of navigating the city of 18 million people.
Women in red saris swept dust away from the last-minute construction work, as barefooted workers hopped onto the tables at the packed press centre to lay wires.
WSF trying to reach out
More than half of the participants at the World Social Forum are from host India, as the anti-globalisation movement tries to branch out from its European and Latin American roots.
"A lot of people in the US are interested in what is happening in the country. The US itself saw the largest demonstrations against the war" in Iraq
Nandita Shah, feminist
The forum is hoping to win more supporters in Asia, which has half of the world's population and gaping inequalities.
But the international audience will also be exposed as never before to Indian social issues, particularly the centuries-old caste system.
More than 138 million Indians belong to the lowest caste, the Dalits, and by tradition are not allowed even to use the same dishes as the upper castes.
"Over 30,000 Dalits are attending the event and they will be the most visible force at the forum," said Ashok Bharti, head of the National Conference of Dalit Organisations.
Among the scheduled speakers at the World Social Forum are Shirin Ebadi, the Iranian rights campaigner and 2003 Nobel Peace laureate, Yossi Beilin and Yasir Abd Rabbu, the Israeli-Palestinian team that drafted the unofficial Geneva peace plan, and Jose Bove, the French sheep farmer and symbol of the anti-globalisation movement.
Several activist groups plan attention-grabbing arrivals, including Japanese pacifists whose "peace boat" is due to dock in Bombay on Thursday and hundreds of Dalits whose nationwide march is expected to culminate at the WSF grounds on Friday.