One day last month, a U.S.-registered Cessna Caravan radioed a mayday call to report engine trouble as it approached this town from Bogota, the capital 240 miles to the north. Minutes later, the plane carrying four Americans and a Colombian army sergeant, who were embarking on an intelligence mission, crashed in the jungle.

The Colombian sergeant and one of the Americans were killed by rebel gunfire immediately after the Feb. 13 plane crash. Since then, thousands of Colombian forces have searched for the three surviving Americans, apparently now in the hands of the Revolutionary Armed Forces of Colombia (FARC), a Marxist guerrilla group designated a terrorist organization by the State Department.

The United States sent 150 U.S. military and civilian officials to Colombia after the crash. The number of U.S. military personnel in Colombia is now 411, the highest number ever stationed there.

But the increased U.S. participation in Colombia's decades-old guerrilla war is likely to last only as long as the Americans are missing, U.S. officials say.

The Bush administration has made it clear that the country will have to shoulder more of the military and financial burden of fighting its guerrilla war. U.S. officials have used the words "exit strategy" and "endgame" during recent visits here to describe Washington's desire to do less in Colombia even as President Alvaro Uribe seeks more U.S. help.

"We're not looking to put more people in here," said Marc Grossman, U.S. undersecretary of state for political affairs, during a news conference Wednesday in Bogota. "This is a Colombian problem that the Colombians will have to solve."

'Colombianization' of War Effort

Uribe's government contends that Washington should view Colombia's guerrilla insurgency as part of the larger war on terrorism. So far, Uribe's appeal has not worked, largely because the primary U.S. goal in Colombia is to fight drug trafficking. Even though peace in Colombia remains elusive, the United States contends it is making progress toward eradicating coca cultivation. Colombia exports 90 percent of the cocaine reaching U.S. shores, and revenue from the illicit trade provides much of the financing for the 18,000-member FARC. Drug money also funds the United Self-Defense Forces of Colombia, a paramilitary force that works alongside the military in many regions.

"You have a government here willing to go all the way, and in the next four years you could really make a difference in this war," Vice President Francisco Santos said in a recent interview. "This alliance must really show itself now because to date it has not been fighting to win, and that's not to say we aren't very thankful for the help that has come."

At the urging of the U.S. Congress, Uribe has taken politically painful steps that will make it easier for Washington to leave Colombia's war. Colombian officials describe the process as the "Colombianization" of the war effort, and recognize it could mean significantly less U.S. help here within the next three years.

Uribe has imposed new taxes intended to raise more than $1 billion this year for the war effort, a longtime Congressional demand. He has outlined plans to add 35,000 soldiers to the ranks, established a civilian intelligence network, and deployed the first contingent of "peasant" soldiers in the countryside.

In exchange, the U.S. Congress included $93 million in its 2003 aid package for a new program to train as many as 800 Colombian soldiers to protect a vital oil pipeline. In 2001, guerrilla attacks on the 500-mile Cano Limon pipeline, operated by Los Angeles-based Occidental Petroleum and the state oil company Ecopetrol, cost the Colombian government $500 million in lost revenue. The loss equaled U.S. aid to Colombia that year -- money Washington wants Colombia to spend on the war effort.

A $1.3 billion U.S. anti-narcotics package doubled the U.S. commitment to this country when it was approved by Congress in 2000, despite concerns about the military's poor human rights record. The Bush administration plans to send an additional $1 billion in military assistance over the next two years. So far, the United States has paid for more than 80 transport helicopters plus programs to train a new anti-narcotics brigade, provide instruction for pilots and prepare elite forces to hunt down guerrilla and paramilitary leaders. The military equipment and training have helped stop the guerrillas from operating in large columns, as they did with devastating effect in the mid-1990s. But the aid has failed to turn the war in the government's favor.

A far smaller percentage of the aid has funded community courts, built rural highways, expanded protection programs for journalists and human rights workers, and a program to coax coca farmers to shift to other crops. Many Colombians and some U.S. lawmakers say the military tilt of the aid package underestimates the social roots of a war that has lasted for generations.

Mindful of those concerns, Congress tied every dollar of Colombian military aid to a specific program or piece of equipment. "I think many of those debates [over U.S. military involvement in a Latin American civil war] have been won now," said Luis Alberto Moreno, the Colombian ambassador to Washington. "But this package still operates on the golden rule -- he who puts in the gold makes the rules."

The American killed by rebels near Florencia was Thomas J. Janis, one of a number of civilian contractors who often experience ground fire as they fly reconnaissance or pilot herbicide-spraying planes over guerrilla-protected coca fields. The body of Janis, 56, a pilot and decorated Army veteran, was found near the Cessna's wreckage with a fatal gunshot to the head. Investigators said he was either shot in an escape attempt or in a futile effort to hold off the guerrillas.

Janis was one of the former military men working for Reston-based DynCorp and California Microwave Systems, a subsidiary of Northrop Grumman. He was under contract to the U.S. Southern Command, which in turn assigned him to work for the U.S. Embassy. The FARC says it considers such civilian operatives mercenaries and thus fair targets. It took responsibility for seizing the survivors, describing them as prisoners of war.

The dead Colombian was Sgt. Luis Alcides Cruz, who worked with Colombian military intelligence. Colombian officials said rules required that a Colombian national accompany intelligence flights. He was found dead alongside Janis, with a bullet wound to the chest. Authorities said the men were killed after the crew managed to set the spy plane on fire to keep its equipment out of rebel hands.

Coca Cultivation Drops

The Cessna's mission was to photograph coca fields for subsequent herbicide spraying operations. A U.S.-trained anti-drug brigade based 15 miles southeast of here at Larandia carries out the aerial eradication program in this region.

The U.S. government says it has succeeded in eradicating some of the coca crop, although there are complaints that the herbicides are also killing food crops, thereby punishing peasant farmers. The CIA reported last week that coca cultivation dropped 15 percent last year, the first decline after a decade of skyrocketing growth. Several state governors in southern Colombia challenged the report, saying it did not include new cultivation sprouting up in other zones.

Uribe's government has been pursuing the U.S. crop eradication program with enthusiasm. In the three months following his Aug. 7 inauguration, 115,000 acres of coca were sprayed in Putumayo province alone -- more than half the national total for the previous year. Critics note the program has pushed thousands of farmers out of the province, strangled the local economy, and encouraged new coca cultivation in the Amazon jungle.

By comparison, former President Andres Pastrana was occasionally reluctant to follow the spraying program as aggressively as U.S. officials demanded.

Gonzalo de Francisco, Pastrana's national security adviser, said the United States applied constant pressure to accelerate the pace of coca spraying, viewing it as cheaper than "alternative development" and crop substitution. Pastrana instead focused on reaching a peace agreement with the FARC guerrillas. "It was not so much a case of a clash of interest, but the fact that our interests did not fit into the same box," De Francisco said. "It was a balance, and I believe by the end much of it had been resolved."

Wiping Out Livelihoods

Luis Carlos Ledezma, 42, traveled to Putumayo in 2001 from the province of Valle del Cauca with his wife and four children to pick coca. But the spraying program wiped out the 40-acre coca plantation where he worked along with acres of intermingled food crops.

Today, Ledezma stoops in the dirt, planting palm seedlings under a thatched roof to guard against errant spraying. Ledezma and his family tried to make ends meet on his wife's $18 weekly pay as a maid. He has gone weeks without a salary.

"Send our regards to the United States," Ledezma said. "And see if they might send us all a visa."

The FARC has taken advantage of the resentment created by the spraying to attract new recruits. FARC leaders say the herbicide spraying violates Colombian sovereignty. But U.S. officials contend the spraying is hurting the guerrillas.

A reduction of 350 metric tons in cocaine exports this year -- a 35 percent decrease -- has deprived the rebels of millions in revenue, officials said. The plan this year calls for eradication of 440,000 acres of coca crops, a figure that accounts for replanted acreage. That would leave about 80,000 acres of coca throughout the country.

But some Colombians say even that level of eradication will not change the dynamics of the guerrilla war.

"I'd prefer that the FARC had more money and fewer people supporting them," said Sen. Antonio Navarro Wolff, a former leader of the demobilized M-19 guerrilla movement. "The FARC may need millions of people to win the war, but they only need thousands to keep it going. These policies give them that and more."

Uribe has failed to link Colombia's guerrilla battles with the Bush administration's global war on terrorism. Colombia's three armed groups are classified as terrorist organizations by the United States, although none are considered to have the "global reach" of al Qaeda and other groups higher on the administration's target list.

"If a deployment is being made because of Iraq, why isn't something similar being thought of to finally solve the problem of drugs and effectively control the Atlantic and Pacific oceans so the traffic of cocaine is stopped between California and Colombia?" Uribe said recently.

But U.S. officials have been signaling to Colombian officials to prepare for the day when the war will again be all theirs to fight.

"We've got requirements, Colombians have requirements, but our goal is to help Colombians defend themselves," a U.S. official said. "What will remain the basis . . . is having Colombians doing this job for Colombians."

Officials have been saying, mostly in private, that Washington will consider its Colombia policy successful once coca cultivation falls beneath 100,000 acres -- something it intends to accomplish by the end of this year -- and the guerrillas are sent back to the distant southern jungles and plains that were once their principal domain.

Colombian officials disagree with that definition of success.

"If someone thinks that by taking coca away you solve our problems, they're crazy," Santos said. "An exit strategy now is a disaster strategy. The only sure thing is that without U.S. help we will not win."

The wreckage of a single-engine Cessna lies on a hillside near Florencia, Colombia. Thousands of soldiers have searched for three U.S. government contractors taken hostage by rebels.