The war on drugs doesn't get more hands-on than this.

Nearly a thousand government workers descended on this rebel-controlled nature preserve Thursday to begin manually uprooting some 11,000 acres of coca plants used to make cocaine.

About 3,000 soldiers provided security for the risky operation — a slow and costly program reflecting the difficulty of winning the U.S.-funded war on drugs. Authorities said they expect the eradication teams to finish the job in three months.

Uniformed peasants hired from across Colombia set out Thursday, small shovels in hand under a blaring sun, into the chest-high, verdant coca fields.

"When we hear gunfire we know what to do: Stop, don't run, and drop to the ground face down," said Jose Luis Aristizabal, 53, who traveled across from Colombia's coffee growing region to take the job, which pays $12 a day.

President Alvaro Uribe ordered Operation Macarena last month after 29 soldiers were killed in an ambush just outside the park's boundaries by the country's main rebel group, the Revolutionary Armed Forces of Colombia, or FARC.

He vowed to remove "every last coca plant" from the park, because he said the rebels were getting rich trafficking cocaine.

For decades, Colombia's guerrillas have enjoyed free run of the 1.6 million-acre park, 105 miles south of Bogota, using the threat of violence to force an estimated 5,000 farmers living inside to grow coca for their increasingly lucrative drug trade, according to the government.

The FARC has not commented on the operation. Analysts said the rebels may have retreated higher into the mountains to avoid direct confrontation.

Military officers left nothing to chance.

"We have a specialized military unit, advancing step by step, looking for mines and making sure eradication crews can work safely," National Police chief Gen. Jorge Daniel Castro said shortly before bending over and uprooting the first coca plant.

The 40-men crews were also accompanied by a team of minesweepers and bomb-sniffing dogs. The campaign is being overseen by 11 observers from the United Nations.

Aerial spraying, common elsewhere in Colombia, could complete the job faster than the three months allotted for the task.

But despite urgings of the United States, Colombia has refused to chemically fumigate any of its 49 national parks and protected areas, 11 of which are believed to contain coca. Castro cited environmental concerns, noting the parks contain dozens of species that exist nowhere else on the planet.

In 2005, the government manually eradicated a record 72,000 acres of illegal drugs, including some in other national parks.

The United States has provided Colombia with more than $4 billion since 2000 — mostly for counternarcotics operations — in an effort to reduce cocaine supplies on U.S. streets by curbing production. But prices for the drug have actually declined in the past six years, which some analysts say shows that supplies remain plentiful.

A report by the White House Office of National Drug Control Policy said despite a record-setting aerial coca eradication offensive, 281,694 acres of the plant remained in Colombia at the end of 2004 — only slightly more than the 281,323 acres that were left over in 2003 after spraying.