THE MOUNTAINS OF EASTERN ANTIOQUIA, Colombia -- The world of Rodrigo 00 is shrinking.

In the brilliant green valley below, explosions thud in the afternoon heat and then fade away. Combat, involving his men. A small plane makes slow loops over his hilltop camp. Intelligence gathering, he says, following the white speck with his eyes.

Rodrigo 00, formerly a leader in Colombia's largest paramilitary movement, now leads his own group of 1,500 men. His forces control part of Antioquia province, defying both the government and his former comrades. (Scott Wilson -- The Washington Post)

Rodrigo 00, his nom de guerre, is the commander of lost causes. With smiling eyes and requisite gallows humor, he is taking a quixotic stand against drug trafficking and has condemned the government's nascent efforts to make peace with a brutal paramilitary force that he once helped lead.

He has lived most of his 38 years in war zones. The zone he now lives in is being taken over by his former comrades in arms. This month alone he has lost 100 men in combat and desertions, all to former friends.

Rodrigo leads an armed faction that has broken with Colombia's national paramilitary federation. He now condemns it as a drug trafficking organization with all the bitterness of a disgruntled former executive. In doing so, a man who acknowledges using harsh anti-insurgency tactics in his region has signed his own death warrant. But he continues trying to build a small-scale utopia here among the rich cattle ranches and deep river valleys of eastern Antioquia, a region that has endured war for 39 years.

"We refuse to give up our ideals and they refuse to give up their interests," Rodrigo told a recent visitor to his camp, 140 miles northwest of Bogota, the capital. "This really is Colombia's problem in miniature. Sometimes you have to fight."

Behind Rodrigo's tenuous stand is the story of the rise and fall of Colombia's paramilitary movement. A witness to its most important chapters, Rodrigo says he thinks the Colombian government, backed by the United States, has misjudged the paramilitary movement and may agree to a peace accord with an organization that he believes has no intention of giving up its most profitable enterprise: drug trafficking.

The regional paramilitary forces that emerged more than a decade ago across northwest Colombia grew into a powerful political and military counterweight to the country's two Marxist guerrilla groups, the 18,000-member Revolutionary Armed Forces of Colombia (FARC) and the smaller National Liberation Army (ELN). Early support for the paramilitary groups came from Colombia's upper classes, mostly wealthy ranchers who were targets of kidnapping and extortion by the guerrillas. But the group's exponential growth over the past three years has been financed largely by Colombia's multibillion-dollar drug trade, the source of as much as 90 percent of the cocaine reaching the United States.

Now the paramilitary confederation, known as the United Self-Defense Forces of Colombia (AUC) has split into at least five regional groups led by powerful commanders like Rodrigo. The fighting among the groups has complicated Colombia's already bewildering war map, as well as President Alvaro Uribe's desire to begin a peace process with the AUC. The State Department, citing drug trafficking and human rights abuses, has classified both the AUC and its guerrilla rivals as terrorist organizations.

Uribe's goal is to remove a key element of Colombia's multi-sided civil war by disarming a paramilitary force that once boasted as many as 15,000 members. Rodrigo, however, says any future negotiations would be used by drug traffickers in the AUC to gain political legitimacy and escape prosecution, their huge profits intact.

Rodrigo withdrew his 1,500-member Metro Bloc from the AUC last September, just before its leaders, Carlos Castaño and Salvatore Mancuso, were indicted by the United States on drug trafficking charges.

In addition to differences over drug trafficking, Rodrigo did not believe the time was right to disarm. The guerrillas he grew up fighting, he says, have shown no signs of weakening, despite Uribe's "triumphalist" claims.

Hoping to undermine a potential AUC peace process, Rodrigo gave The Washington Post a copy of an assessment prepared for the president as he considers whether to proceed with formal negotiations. The analysis, which is dismissed by Uribe's peace commissioner, Luis Carlos Restrepo, as "not an official document," concludes that "it is impossible to distinguish between the self-defense groups and narcotrafficking organizations." Members of the Colombian government verified the findings, but nonetheless remain committed to pursuing a peace process with the AUC.

"Those who do not take part in the peace process we are going to go after," Vice President Francisco Santos said in an interview. "This is the last window of opportunity for them."

Like many paramilitary commanders, Rodrigo was once a Colombian army officer. He grew up in Medellin, a crossroads of Colombia's drug trade, and studied at the Jesuit San Ignacio School.

As a lieutenant in the late 1980s, he ran anti-guerrilla patrols in the central Magdalena River valley, only about 25 miles from his current camp. At the time, the region's inhabitants were sympathetic to the FARC. Lacking civilian support, Rodrigo's units were savaged in guerrilla ambushes. So he began forcing young men who had avoided Colombia's obligatory military service to work as guides or face jail time.

"It was very good for my operations, but very bad for my résumé," Rodrigo said of the tactic, which got him suspended. "I knew I'd never make general after that, so I quit."

Among the civilians helping the military were two brothers, Carlos and Fidel Castaño, whose father had been killed by the FARC. "They did not need to be forced to help," Rodrigo said wryly. Fidel, the older brother, was a swaggering rancher and emerald speculator who tempered his bloodthirsty anti-guerrilla attitudes with a populist political vision of how to end the long war. Rodrigo went to work for him in 1989.

After helping the Colombian police and the U.S. Drug Enforcement Administration hunt down and kill the Medellin drug kingpin Pablo Escobar in 1993, the Castaño brothers concentrated their paramilitary army in the northern province of Cordoba where Fidel owned more than 25,000 acres of ranch land. He began parceling out property to peasants in an effort to build a bridge between the region's small economic elite, who supported the fledging paramilitary groups, and the far larger pool of rural poor, many of whom supported the guerrillas.

The Castaños envisioned an authentic middle class that would deprive the FARC of its civilian support. Rodrigo still subscribes to that political prescription for Colombia's war. But he said AUC supporters, particularly drug lords who own huge tracts of prime land in the provinces of Cordoba and Antioquia, have opposed reform at every step.

"Any peace process with the AUC should not be measured by the number of men disarmed, but by the amount of land turned over to the government by the narco-traffickers," he said. In an irony not lost on Rodrigo, land reform has also long been a key demand of Colombian guerrilla groups.

The AUC's efforts to win popular support in southern Cordoba came under assault from the FARC in the mid-1990s, as the guerrillas began forming lucrative alliances with drug traffickers to finance their insurgency. Carlos took over the paramilitary group in 1994 and began looking for ways to achieve military parity with the guerrillas. Rodrigo remained a top lieutenant.

At around that time, Colombia's two major drug cartels were waging a bloody struggle for control of the industry after the collapse of Escobar's Medellin-based organization. Rodrigo said the leaders of one of the trafficking groups came to Castaño with a deal in the late 1990s: Help us and you can earn money for your war machine.

Among them was a man named Diego Fernando Murillo Bejarano, also known as Don Berna, who was fleeing a contract on his life taken out by the Cali cartel. A former Medellin cartel figure, he is now the third-ranking member of the AUC, using the pseudonym Adolfo Paz. He is also Rodrigo's nemesis. His potent Medellin-based paramilitary unit is pounding Rodrigo from the west.

"Their argument was, this is the only way we are going to defeat the guerrillas," Rodrigo recalled. "But I told them our job is not to defeat the guerrillas, but to help the state defeat the guerrillas. And narco-trafficking only weakens and corrupts the state."

He lost his argument.

"Castaño is a noble guy," Rodrigo said. "He's the only political guy in an organization filled with drug traffickers. But this was the worst possible decision he could have made. It was the breaking point."

By Rodrigo's account, the drug traffickers started influencing the AUC's military tactics. Rodrigo said Castaño was pressured to begin taking over key drug-producing regions and the overland corridors needed to move shipments out of the country. With a force far smaller than the FARC's, wiping out the guerrillas' civilian supporters was the most efficient way to do this. Huge civilian massacres became the AUC's trademark.

At the same time, Rodrigo said he discovered that many drug traffickers working for the FARC were no longer AUC military targets. The AUC was now relying on the same traffickers for money, bringing the paramilitaries and the FARC into a de facto alliance that he predicts will perpetuate the war.

"The FARC still talks like guerrillas, lives like guerrillas and acts like guerrillas," Rodrigo said. "The AUC talks like narcos, lives like narcos and acts like narcos."

Rodrigo says he has not allowed drug cultivation in his region, raising money instead through obligatory taxes on merchants and the sale of black-market gasoline in the 45 counties of eastern Antioquia province that are under his control. Although few massacres have been attributed to the Metro Bloc, small-scale killings of civilians carried out by his men have become routine in many towns under his control. There is no pending order for his arrest. Few people even know his real name.

His wife and 9-year-old daughter went into hiding after receiving threats from the AUC, a danger he said his family never faced when he was fighting the guerrillas. A regional commander of Colombia's military, he said, has been offered $1 million by a rival paramilitary group. They want to secure safe passage so that a column of their fighters can attack Rodrigo's camp. So far the officer has refused. He is one of many military officers whom Rodrigo still considers a friend.

It is hard to see how Rodrigo will survive much longer against his former comrades, who have helicopters, private planes and endless sums of money at their disposal. Rodrigo acknowledges his delicate position but says he will survive. "Fighting the guerrillas was child's play compared to what I face now," he said.

Rodrigo contends that Colombian history is on his side. "I have seen drug cartels rise and fall before, and these guys are doing the exact same thing," he said. "Their days are numbered."