Mar Del Plata, Argentina ? Waving communist flags and images of famed revolutionary Che Guevara, thousands of people opposed to President Bush and free trade protested Tuesday at a “People’s Summit” ahead of this weekend’s fourth Summit of the Americas.

Arriving in buses and minivans at the seaside resort of Mar del Plata, the demonstrators gathered at a drab concrete sports complex several miles from the luxury hotel where leaders of 34 Western Hemisphere nations will meet Friday and Saturday.

“This is a chance for the real people to hold their own summit,” said Wayra Aru Blanco, a 33-year-old Bolivian Indian.

Protesters will spend days airing grievances from the Iraq war to free trade policies they say enslave Latin America workers. They are hoping to draw 50,000 people for their highlight event – a protest Friday a day after Bush arrives.

Riot police guard a security fence Tuesday that secures the area where leaders attending the Americas Summit will gather this week in Mar del Plata, Argentina.

Venezuelan President Hugo Chavez, a leftist whose government has used the country’s vast oil wealth on social programs for the poor, was invited to attend the march. Chavez, an outspoken critic of free trade, has strained relations with Washington and regularly claims the United States is trying to overthrow his government, an accusation U.S. officials have dismissed.

Violent protests broke out in the capital of Buenos Aires over poor commuter train service, and authorities blamed the unrest on leftists and labor activists, though there was no immediate indication that it was related to the impending anti-Bush demonstrations.

Fidel Castro is the only Latin American leader who will not attend. He is not permitted to participate because communist Cuba is not a member of the Washington-based OAS, which organizes the summit.

Heavy security precautions were being taken at the summer resort 230 miles south of Buenos Aires, with some 10,000 police and security forces already deployed in Mar del Plata.