Thousands of activists gathering in Venezuela's capital for a six-day World Social Forum that opens Tuesday include anti-war protesters, Indian leaders, campaigners against free trade and environmentalists. But they are all united by one thing: their opposition to President Bush.

The forum, which was set to begin Tuesday afternoon with an anti-imperialist march through Caracas, was being promoted by Venezuelan President Hugo Chavez, who has frequently clashed with the United States and accuses it of plotting to overthrow him. He is also one of the leading voices of the new left sweeping across Latin America.

Organizers said more than 60,000 people had signed up to attend and tens of thousands more were expected at the forum, about half of them from outside Venezuela.

Anne Hess, an activist from Norway, said she was attending the meeting to protest Bush and British Prime Minister Tony Blair, who led the 2003 invasion of Iraq.

"We need to stop the war in the Middle East," she said Monday. "We need the whole world out in the streets again to stop Bush and Blair, and their crazy imperialist dreams."

Chavez is expected to address activists on the sidelines of the conference. He has recently strengthened ties across South America as left-leaning leaders have won power in countries from Argentina to Bolivia.

"Venezuela has become an epicenter of change on the world level," Chavez said Friday, referring to the event in a speech. "That's why (U.S.) imperialism wants to sweep us away, of course ... because they say we are a bad example. But they haven't swept us away and they won't."

Chavez has used a windfall in oil profits to funnel millions of dollars into programs for the poor -- something that has made him an inspiration for like-minded activists. But organizers of the forum emphasized the event was not intended as a giant rally for Chavez, though it was backed by government funding as in past years.

The World Social Forum was first held in Brazil in 2001 and coincides each year with the market-friendly World Economic Forum of political and business leaders in Davos, Switzerland.

Protests were staged around Switzerland over the weekend ahead of the economic forum, which starts Wednesday. That meeting will be attended by Germany's new chancellor Angela Merkel, Pakistan's President Pervez Musharraf and U.N. Secretary-General Kofi Annan, as well as more than 700 chairmen and CEOs from the world's leading companies.

Those at the social forum, in contrast, traditionally criticize free trade and denounce the evils of capitalism -- stances that closely mirror Chavez's socialist views.

"The U.S. government, especially under the Bush administration, has been trying to force its own economic polices on developing countries, and I think all of us here agree that must stop," said Jeff Monahan, a 32-year-old organic farmer from Battle Creek, Mich., who was helping erect canopies in a city park where thousands will camp out in tents.

Some 2,000 events -- including seminars, speeches, concerts and craft fairs -- will be held across Caracas during this week's forum. Well-known speakers include Uruguayan writer Eduardo Galeano, Argentine Nobel Peace Prize winner Adolfo Perez Esquivel and American anti-war activist Cindy Sheehan, whose son was killed in Iraq in 2004 and who set up a protest camp near Bush's ranch in Texas last year.

It was not clear whether other leftist leaders from Latin America would come. Some activists said they hoped to see Presidents Evo Morales of Bolivia or Fidel Castro of Cuba. Brazil's Luiz Inacio Lula da Silva initially was expected, but then said he would not come.

On Monday, Venezuelan authorities in Caracas closed a main thoroughfare and lined it with displays where government officials handed out pamphlets about Chavez's social programs. Street vendors sold T-shirts, keychains and watches bearing images of Chavez, Castro and revolutionary hero Che Guevara.

"It's nice to see the energy that's going here," said Catharine Quinn, a 34-year-old health activist from Chicago, who picked up a Che watch and a Chavez flashlight.

This year's social forum is being held in three spots around the world, including one ending Monday in Bamako, Mali, and another two months from now in Karachi, Pakistan. The Venezuela forum is the main event and the smaller forums are meant to make it more accessible to people in other regions.