Their fuselages flashing in the sun, two airplanes lazily circled over fields of coca, ready to dump a load of herbicides onto the robust, green bushes used to make cocaine. Rebels waited below. 

Crouching behind fences, tree stumps and the coca itself, fighters from the Revolutionary Armed Forces of Colombia, or FARC, opened up on the two Vietnam-era planes with M-16 and Galil assault rifles, the crackle of automatic weapons fire splitting the afternoon silence. 

During the action Friday, witnessed by an Associated Press team accompanying the rebels through the coca fields near the southern village of Penas Coloradas, neither of the U.S.-made OV-10 airplanes was shot down. But the camouflage-clad leftist guerrillas considered it a victory: The unprotected aircraft veered off without releasing their cargo. 

President Clinton's visit to Colombia on Wednesday and a $1.3 billion U.S. aid package aim to drive the rebels from the drug fields. Under the plan, 60 U.S. combat helicopters will escort fumigation planes and ferry U.S.-trained anti-narcotics troops into drug-producing plantations that cover vast areas of southern Colombia. 

FARC rebels, as well as a rival right-wing paramilitary group, protect the crops of coca and poppy, from which heroin is made. The rebels have vowed to fight the anti-drug offensive. 

Critics contend the so-called Push into Southern Colombia, expected to get into full swing next year, will derail fledgling peace talks and draw the United States directly into Colombia's 36-year-old guerrilla war. 

U.S. officials insist their only interest is in fighting drugs but express growing concern about the 15,000-strong FARC, which has used proceeds from the drug trade to better arm itself and to dominate a large part of the countryside. 

FARC commander Alfonso Cano called the planned offensive a veiled counterinsurgency plan and a symbol of President Andres Pastrana's subservience to Washington. 

"The United States needs an excuse to continue to play the role of the world's policeman, and now that excuse is (fighting) drug trafficking," said the bearded rebel leader in an interview in San Vicente del Caguan, a town a four-hour riverboat ride north of Penas Coloradas. 

Nationwide, many Colombians support the anti-drug push. But in Colombia's coca-growing regions, hundreds of thousands of poor coca farmers, itinerant harvesters and small-time merchants do not. 

In Penas Coloradas, a grimy settlement on the brown and windy Caguan River, 280 miles from the capital Bogota, coca is the economy's driving force and the FARC the only law and order. The rebels take their cut of the cocaine production process while serving as a de facto government. Liquor sales are forbidden between Monday and Friday. Theft and drunkenness are punished. Prostitutes at the town's Great Saigon bar must take AIDS tests. 

Before the fumigation planes made their abortive spraying attempt, the local rebel commander — known as Herley — said the coming offensive will provide the FARC with an ample recruiting base among farmhands who could lose their livelihoods as a result. 

"How many enemies are created when you take away the food from someone's children" the rebel, a 22-year FARC veteran with long, soiled fingernails and a bloodshot glare, asked as he strode through the coca fields. 

Later, as the fumigation planes flew overhead, he rested the barrel of his rifle on a tree stump, aimed at the aircraft, and carefully squeezed off a few rounds. 

For the farmers in Penas Coloradas, as in much of the rest of impoverished, rural Colombia, there are few viable alternatives to making a living than growing coca. They are skeptical of government pledges that the anti-drug offensive will be accompanied by loans and other assistance to help them grow legal crops. 

"The government doesn't even know we exist," fumed Miguel Hernandez, whose four-acre coca plot was fumigated two times last week, wilting banana trees mixed in with the coca. 

Only about a tenth of the U.S. aid plan would provide funds for alternative development projects. 

While the cocaine trade nets huge profits for those further up the international drug chain, the small-time farmers who grow coca near Penas Coloradas make very little. 

Jose, a farmer who turned to coca four years ago after working for years as a migrant coffee picker, said he earns only about $375 a month in profits off his 12 ½ acres of coca. He didn't give his last name for fear of having problems with the law. 

Standing in a wooden shack at a bend in the Caguan River, he intently watched local men commissioned by drug cartels test the purity of his football-sized bag of "coca base" — a semi-processed form of cocaine. One of the men then handed Jose a wad of cash. 

"It's not honorable work," Jose said sheepishly. "But here in Colombia we have to eat however we can."