By Hugh Bronstein

BOGOTA, July 5 (Reuters) - Hundreds of thousands of Colombians headed for the streets on Thursday to show outrage at last week's news that 11 provincial politicians had been killed while held hostage by leftist rebels.

Demanding freedom for other kidnap victims, including French-Colombian politician Ingrid Betancourt and three American defense contractors, they marched in small towns and cities. They were to be joined by protests in other Latin American countries, France, Spain and the United States, organizers said.

Public employees were given the day off to participate. They clamored for a hostage swap, but the government and Colombia's main rebel group appeared far away from starting talks that might lead to an exchange.

"Marching is a way to unite for the freedom of the kidnap victims rather than acting as an isolated chorus, singing sadly," said Colombian music star Juanes, who planned to march in his home town of Medellin.

"The only way to negotiate peace is with those who have done wrong. If we have to sit down and negotiate with them then we have to," he said.

Betancourt was captured during her 2002 presidential campaign. U.S. defense contractors Thomas Howes, Keith Stansell and Marc Gonsalves were taken by the rebels during a 2003 drug-eradication mission.

Despite pressure to swap these and other hostages for guerrillas held in government jails, President Alvaro Uribe stiffened his refusal to grant guerrilla demands that he establish a New York City-sized rural zone with no government troops where an exchange could be negotiated.

"We cannot accept safe-haven zones and we cannot accept rebels being released from prison only to go back to killing people," Uribe said. Uribe, whose father was killed more than 20 years ago in a botched rebel kidnapping, has long received public support for his tough stance against the guerrillas.

Thursday's edition of leading daily El Tiempo was wrapped in a supplement page with the headline "Solidarity Breaks the Chains." It featured the names in fine print of thousands of kidnap victims still being held throughout the country.

SECRET JUNGLE PRISONS

Last week the Revolutionary Armed Forces of Colombia, or FARC, said 11 provincial politicians held for more than five years had been killed in a cross fire when an unidentified military group attacked their secret jungle prison.

But Uribe says state security forces were nowhere near the camp and accuses the rebels of murdering the men, in an incident that has shocked the country.

He demands that the FARC turn over the bodies of the 11 hostages so the circumstances of the deaths can be determined.

Colombia was stunned in 2002 when the guerrillas kidnapped the lawmakers from a government building in Cali by masquerading as soldiers and calmly escorting them onto a bus, saying they were being evacuated due to a bomb scare.

The FARC was organized in the 1960s to force land reforms meant to close the wide gap that divides rich and poor in this Andean country. But even left-wing politicians say the group has scant popular support.

In the 1980s, rich Colombians organized paramilitary militias to ensure protection from FARC kidnappings and land grabs. By the late 1990s, both groups had become involved in cocaine smuggling and took to murdering peasants suspected of cooperating with the other side.

Thousands are killed in the war every year.

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