MAMPUJAN, Colombia » The jungle owns Mampujan, this once-prosperous farming town near the Caribbean coast that has become a symbol of Colombia’s descent into lawlessness.

Paramilitary fighters invaded the town in early 2000 and accused residents of sympathizing with leftist guerrillas. They rounded up hundreds of people in the main square, threatened to kill them and ordered them to depart their homes and farms. The residents all fled.

Today, the square is choked with weeds. Bats roost in the one house that still has a roof. Green paint peels from a blackboard in the derelict schoolhouse.

Bringing people back to Mampujan and other rural communities that have been terrorized for decades by guerrillas, paramilitary groups and drug traffickers has become a priority for the Colombian government, which has begun an ambitious nationwide program to give millions of acres of land back to tens of thousands of displaced farmers. But the effort has been complicated both by the logistical difficulty of sorting out who owns long-abandoned or disputed plots and the extreme fear that still lingers among those who left.

"The love I have for my land, I haven’t lost it," said Marquesa Lopez, 61, recalling the 64 acres where she and her family grew yucca and corn and raised cattle. Like other displaced residents of Mampujan, she eventually moved to a makeshift settlement outside the nearby town of Maria la Baja.

"I had my family, my banana trees, my coconut palms, my chickens," she said. "Now I want to live that life again."

In October, a special agrarian judge gave Lopez and her husband, Carlos Arturo Maza, and 13 other Mampujan families title to the land they lost, the first such decision under a new land restitution law that is the centerpiece of the government’s effort to address the effects of years of violence and longstanding inequalities in rural areas.

The effort is unfolding as the government starts peace talks with the country’s largest guerrilla group, the Revolutionary Armed Forces of Colombia, or FARC.

The unequal distribution of land in Colombia’s impoverished countryside, where poor farmers were pushed aside or exploited by wealthy landowners, was a major factor in the creation of the FARC nearly 50 years ago, and it has continued to fuel the conflict.

Now, the government sees the land restitution law as a crucial lever at the bargaining table.

"This is something that takes away one of their banner issues," President Juan Manuel Santos said in October.

But for that to be true, Santos has to deliver on the program’s promise, an enormous and intensely complex task.

The government has received more than 27,000 claims for close to 5 million acres of land, and more are pouring in. Each claim must be investigated and then considered by a judge. Many are dauntingly complex, involving ownership disputes with little or no documentation.

"Of course it’s complicated, and it’s difficult, but what was the alternative?" said Juan Camilo Restrepo, the agriculture minister. "To do nothing? Which is what some people wanted to happen, to do nothing and validate with silence and inaction 25 years of land takeovers."

Critics say the process has been too slow and unwieldy, and they question the government’s commitment to face down powerful landowners and their political allies.

"It would be very sad if this ends up where you have 10 cases that will go down in history where, yes, we were able to do this, and thousands of cases in which it couldn’t be done," said Ivan Cepeda, an opposition lawmaker.

Restrepo said that about 300 people have reported being threatened in relation to land claims under the new program and that the government has taken measures to protect 159 of them, in many cases providing bodyguards.

Mayerlis Angarita, 32, an activist who visits remote villages encouraging people to make land claims in the region of low mountains around Mampujan, called Montes de Maria, travels with a government-assigned bodyguard because of repeated threats.

On Aug. 28, a gunman shot at her on the streets of her hometown, San Juan Nepomuceno. She was not hit but was injured while running to take cover.

"Peace is built here on the back roads," she said, as her bodyguard drove a bulletproof SUV in an area where former paramilitary fighters still enforce a nighttime curfew to keep local roads clear for drug trafficking. "They cannot force us out of here."

But many activists have fled. In recent weeks, menacing fliers have been circulated, signed by a group called the Anti-Restitution Army. Activists believe the fliers are linked to landowners and their allies among the paramilitaries and drug traffickers.

"The armed groups and criminal mafias that were involved in the displacement in the first place continue to operate," said Max Schoening, the Colombia researcher for Human Rights Watch. "Unless you dismantle those groups and hold them accountable, you’re not going to eradicate the underlying source of threats and intimidation."

Mampujan was a likely starting place for the restitution program because much of the farmland remains unoccupied and there is no one to dispute the residents’ ownership. But many other land claims involve parcels currently in the hands of owners who will fight to keep them, including guerrillas and former paramilitary chieftains.

In many cases, farmers sold their land under pressure, often at fire sale prices.

Fanny Martelo and her husband, Ismael Montes, fled a 113-acre farm in a hamlet called Palmito in 1992. Martelo explained that her husband and other farmers were summoned to a meeting in 2008 by a company that had bought a portfolio of delinquent government land loans. She said the farmers were pressured to sell to pay off the debt.

Martelo’s husband agreed to sell to a Medellin businessman, Ruben Dario Velez. As part of the deal, in which Martelo and her husband received about $5,500 in cash, Velez agreed to pay off the loan and associated legal fees, Martelo said.

She said that Velez then contacted the family in October after she and her husband filed a claim under the land restitution law. He threatened to have them put in jail and vowed to hold onto the property, she said.

Velez denied her account. Lawyers with the government restitution unit in Carmen de Bolivar, where Martelo and her husband now live, said they were investigating several claims involving Velez and other buyers to see if they represented coerced land sales.

Those who have recovered their land still face challenges.

In Mampujan, there is no electricity, no schools or health clinic. Even if residents return, they will face the same problems holding back small farmers across Colombia: lack of capital, machinery and modern farming methods.

The government has promised help, but doubts remain.

"If we have the land but we don’t have help, with empty hands what are we going to do?" said Joaquin Mata, 67, a former resident who is still waiting for a ruling on his land claim.

© 2012 The New York Times Company