* Indigenous people demand army and FARC guerrillas leave
* Former President Uribe says soldiers humiliated (Releads, adds details, quotes)
By Helen Murphy and Jack Kimball
BOGOTA, July 18 (Reuters) - Colombian security forces clashed on Wednesday with indigenous activists who stormed a hill-top military base in the volatile south as critics lambasted President Juan Manuel Santos for failing to protect troops.
Riot police using tear gas and armored vehicles battled youth hurling stones, wounding at least 26 protesters and killing one, in the second day of violence in Cauca province, a FARC rebel stronghold, an indigenous group and local media said.
Bloodshed in Cauca - one of the hottest areas in conflict-wracked Colombia - has generated more criticism of Santos, whose once-commanding approval ratings have fallen in recent weeks due to a resurgence in guerrilla attacks.
Indigenous leaders have called on both government troops and the Revolutionary Armed Forces of Colombia (FARC) to abandon the jungle-covered mountains so they can rebuild their lives after years of bloodshed that killed dozens from their community.
Machete-wielding indigenous activists on Tuesday overtook a military position in Toribio municipality of Cauca, jeering and waving sticks as they dragged soldiers from trenches. FARC rebels had shot at troops from the hills.
"We profoundly regret having to use force to restore our constitutional rights. This could have been avoided if the army heeded our request in due form and the government had ordered them to leave," the Association of Indigenous Councils of Northern Cauca said in a statement.
An indigenous leader in a neighboring municipality told local media that residents had surrounded at least 30 soldiers after one person was killed at a checkpoint.
Santos said he would not remove soldiers from the area.
"We will not permit attacks against those who are defending us, our soldiers," he said. "Troops have the firm order not to give up one centimeter in Cauca or any part of national territory."
Santos was to return to Cauca on Wednesday.
Last week, helicopter gunships strafed rebels in the hillside and removed explosive devices to secure the area before he arrived to talk about security and launch a drive to spur further investment into the region.
Front page newspaper photographs on Wednesday of a soldier crying and another being chased by local residents gave fodder to political rivals of Santos who want to paint the former defense minister as out of touch with security on the ground.
"Will this picture matter for Santos' re-election?" the political news website La Silla Vacia bluntly asked about a picture of a soldier being forcefully carried out of a trench.
Santos swept to office in 2010 promising to build on the security advances that began under former President Alvaro Uribe. A U.S.-backed offensive weakened the FARC and drug gangs, making Colombia safer and fostering foreign investment.
Santos has not said whether he will run again in 2014, but ally-turned-foe Uribe is already promoting potential rivals - a move that could split the ruling coalition.
"How sad that Colombia's going back to a lax ideological stance against violence," Uribe said on Twitter. "What's the plan for security if our soldiers are allowed to be humiliated."
The FARC, which has battled the government for half a century, has holed up in the inhospitable jungle terrain of Cauca for decades as successive governments deployed thousands of troops to oust them.
In late 2011, Colombian forces dealt the rebels a major blow, killing FARC leader Alfonso Cano in Cauca. The province had become an area of intense military operations since Cano took over the insurgent group three years before.
Since then, rebels have fought back, stepping up attacks on economic targets like oil and mining installations and threatening the government's drive to restore Colombia's image. (Editing by Vicki Allen)