BY JUAN O. TAMAYO

 SANTANA, Colombia -- Coca grower Luís Nectario Gómez can almost feel the
 rumble of war approaching as U.S.-financed army troops prepare to blitz into the
 heart of Colombia's guerrilla-dominated cocaine industry.

 ``One fears what's coming,'' Gómez said with a terse frankness as he walked his
 small field in the southern Putumayo state, one-sixth the size of Florida but home
 to nearly half of Colombia's 300,000 acres of coca.

 President Clinton's scheduled visit Wednesday to the city of Cartagena will show
 his support for Plan Colombia, a counter-narcotics onslaught backed by a $1.3
 billion U.S. aid package officially released last week.

 But soldiers and rebels in Putumayo, the offensive's first target, have been
 readying for a battle that might decide the future of an industry now supplying 90
 percent of all the cocaine sold to U.S. consumers.

 The leftist Revolutionary Armed Forces of Colombia, called FARC, has reinforced
 its ranks in the region from 900 to 1,500 since May, and another 500 reportedly
 arrived last week, Army and Defense Ministry officials said.
 YOUNG ARMY

 FARC rebels are forcing boys as young as 15 to join their ranks and requiring
 older peasants, men and women, to undergo weapons training to be ready for the
 upcoming ``gringo invasion,'' municipal and church officials said.

 Firefights between soldiers and guerrillas rose five-fold in the past few months and
 worse is expected, said Col. Gabriel Díaz, commander of the region's main army
 base in Santana, 550 miles southwest of Bogotá.

 U.S. Special Forces are training a new army anti-narcotics battalion 100 miles
 north of Santana, and the military will soon move 18 UH-1N ``Super Huey''
 helicopters into the region to help assault guerrilla-defended coca plantations
 while police crop-dusters spray herbicides.

 Right-wing paramilitary groups estimate that 350 to 800 men are also recruiting
 and pushing into FARC strongholds in Putumayo -- sometimes battling the
 rebels, more often executing suspected civilian supporters of guerrillas.

 Some families have quietly begun sending their children to safer areas, and
 neighboring Ecuador has drawn up plans to receive up to 5,000 refugees across
 the border when Plan Colombia kicks into high gear.

 Caught between soldiers, rebels and paramilitaries, and fearing that the
 fumigation will also kill their food crops and farm animals, Gómez and 488 other
 small-time coca growers around Santana last week offered to uproot their own
 bushes -- if the government gives them enough aid.

 Colombian officials say there's no set date for the start of Plan Colombia's push
 into Putumayo, the opening shot in a five-year plan to eradicate half the nation's
 coca and opium poppy fields.
 IN PLACE

 ``It'll take three months to put the military and social components in place . . . but
 that doesn't mean we won't do large operations down there before,'' Defense
 Minister Luís Fernando Ramírez said in an interview.

 The plan combines stepped-up fumigation and military interdiction with economic
 development programs to wean peasants away from illegal crops, as well as
 efforts to strengthen government agencies in the countryside.

 Ramírez said the initial phase of the fumigation campaign will target the estimated
 70 percent of Putumayo's coca plantations that are larger than 25 acres, in hopes
 that smaller farmers will voluntarily uproot their bushes.

 U.S. critics of Washington's growing military involvement in Colombia -- the
 biggest in Latin America since El Salvador in the 1980s -- warn it will suck
 America into a counter-insurgency war in a nation twice the size of Vietnam.
 INTENSIFY WAR

 Plan Colombia will also intensify the war, upset ongoing government peace talks
 with the FARC and shower herbicides on a richly biodiverse Amazon basin region,
 local opponents predict.

 ``Kennedy sent us hospitals. Bill Clinton sends us rifles,'' one Putumayo farmer
 shouted at a passing group of foreign journalists, referring to President John F.
 Kennedy's Alliance for Progress in the 1960s.

 President Andrés Pastrana's government acknowledges Plan Colombia will be an
 uphill fight, but insists it is the best chance to attack a narcotics industry that is
 eroding the government through corruption and strengthening the rebels through
 massive protection payoffs.

 ``We have a window of opportunity here, because I don't think it's easy to find
 another 300,000 acres with so little government presence, the right soil and a
 natural ally for narco-traffickers, the guerrillas who protect the fields,'' Ramírez
 said.
 TAKING TOLL

 But a look at Putumayo shows just how difficult Plan Colombia's opening ``push
 into the south'' will be.

 ``How else can I feed my family?'' asked Gómez, 54, whose 7.4-acre coca plot is
 part of an 86-acre field farmed cooperatively by 18 families a five-minute drive and
 a short walk from Col. Díaz's heavily sandbagged headquarters.

 From a military helicopter flying at 4,500 feet to avoid guerrilla gunfire, the vistas
 are of stunningly vast expanses of coca bushes, many deep in the Amazon
 jungle, two just off the airport runway in the town of Orito.

 Once home to cattle ranchers and hardscrabble farmers -- it had three people per
 square mile in 1990 -- Putumayo today is little more than a cocaine factory and
 bloody battleground for the army, FARC and paramilitaries.

 Television satellite dishes sprout from the tin roofs of peasant homes, farmers
 sport gold wrist chains and cultivate so much coca that eggs, corn and plantains
 must be imported from neighboring Ecuador.

 ``This is a coca town,'' said Manuel Alzate, mayor of Puerto Asís, the state's
 largest town with 38,000 people, a rough-hewn kind of place with lots of loud bars,
 discothéques and cheap brothels.
 PAVED STREETS

 Motor scooters and trucks dominate its few paved streets, and the town was
 connected to the national electricity grid only 18 months ago.

 Half its homes still lack running water, two-thirds have no sewers.

 Of the 65 deaths reported in town this year 52 were violent, most the work of
 paramilitary or FARC hit squads. Of the previous five mayors, three were killed
 after leaving office, two by guerrillas, one by ``paras.''

 ``It is a massacre, drop by drop,'' said parish priest Luís Alfonso Gómez. One of
 his predecessors was assassinated by the FARC while saying Mass in 1998,
 another left town with ulcers apparently caused by the pressures.

 Army troops and paramilitary gunmen control the town in what Alzate, 60, a cattle
 rancher and former priest excommunicated in the 1960s for his liberal politics,
 calls ``a peaceful coexistence.''

 Díaz said he does not tolerate paramilitaries and reported his troops killed five in
 combat this year. Soldiers have raided one known ``para'' house in Puerto Asís
 four times but found nothing because sympathizers in town tip the gunmen, he
 added.

 The FARC controls most of the countryside, and its territory starts a five-minute
 boat ride from Puerto Asís across the café-con-leche colored Putumayo River,
 which marks the border with Ecuador and Peru further downstream.
 TAXING THE TRADE

 With 1,500-2,000 fighters in Putumayo and 17,000 in all Colombia, the FARC
 draws about 60 percent of its income -- $300 million to $500 million a year -- from
 ``taxing'' the cocaine trade.

 Paramilitaries are also into the protection racket, and Díaz said that of the 12
 cocaine refineries raided by his troops this year, nine were protected by FARC
 fighters and three by paramilitary gunmen.

 ``This is not an ideological war. This is an economic war,'' said Díaz.

 It is indeed those economics that have made thousands of Putumayo families
 turn to coca cultivation. One hectare of the bush -- 2.47 acres -- can produce an
 annual profit of $2,700, a princely sum in a region where a good day's salary is $7
 a day.

 ``With the income from this I can send the kids to school, maybe get the
 medicines we need,'' said Luís Nectario Gómez as he showed visitors around his
 neat rows of head-high coca bushes, just sprouting new leaves after the last
 harvest.
 A COMPROMISE

 Gómez was one of 489 small-time coca farmers from the Santana area who last
 week volunteered to uproot their plants if Pastrana's government comes across
 with enough economic aid for themselves and the region.

 ``We're all tired of coca,'' said schoolteacher Ernestina Cifuentes, 42. ``Too many
 widows. Too many widowers. Too many orphans. But without that money we
 cannot live.''

 Alzate and Putumayo Gov. Jorge Devia have embraced the proposal, arguing it is
 preferable to massive fumigations rumored to kill food crops, farm animals and
 even humans even though Colombian officials insist the chemicals are safe.
 SOME SKEPTICAL

 FARC commanders have not said whether they will support voluntary eradication
 -- a key requirement if it is to succeed. And some government officials remain
 skeptical. ``They know that if they don't eradicate in the next month I will throw
 them in jail,'' Díaz said.