SAN FRANCISCO, PERU — JUST minutes upriver from this ramshackle, high-jungle town, bright-green patches of crops dot the steep surrounding hillsides.
It seems there is only one activity in the Apurimac Valley: coca growing. Outside one house lies a carefully tended nursery of seedlings; farther on, a man plants a freshly ploughed slope; everywhere, thick carpets of coca leaves dry in the sun.
Last year, this valley produced 16,000 tons of coca leaf, the raw material from which cocaine is produced, according to official US statistics. This is just under 10 percent of national coca output. The US State Department estimates that Peru produces 57 percent of the world's supply of leaf, equivalent to about 551 tons of pure cocaine.
''For years, coca has been the only crop that pays in the valley,'' says Carlos Barrantes, secretary-general of the Apurimac federation of coca-growers, or cocaleros. Like many other local farmers, he grows about five acres of coca for cash in an otherwise almost unproductive 25-acre plot.
''Coca requires little investment, the buyer comes to your door and pays cash,'' Mr. Barrantes says. ''Although we understand coca creates problems in the US and elsewhere, you can't blame peasant farmers for growing what is easiest and most saleable.'' He believes Apurimac coca production expanded by over 30 percent last year.
From the mid-1980s, Sendero Luminoso (Shining Path) Maoist guerrillas terrorized the valley, serving as intermediaries between the coca growers and dealers. Elected officials were assassinated; roads fell into disrepair and weeds strangled traditional cocoa and coffee crops.
Now that the battle against Shining Path is apparently won, Peruvian security forces have attacked the narcotics problem with unusual energy in the past few months. Gen. Gustavo Bravo, head of Dinandro, Peru's antinarcotics police force, is calling 1995 ''the year of head-on battle against drug trafficking.''
Between January and March, the armed forces and Dinandro downed or captured 11 drug-transporting aircraft. More than seven tons of coca and cocaine were confiscated in the same period -- 60 percent of last year's total haul. A major Peruvian drug cartel has been deactivated.
Along the Apurimac River, several new military bases have been installed. Soldiers search traditional wooden longboats, which used to include coca leaf or paste and the processing chemicals.
Controls seem to be working. ''They're far too strict,'' complains Rosario, who migrated from the high Andes to set up a makeshift riverbank bar. ''I expect to make real money here, but the Army has killed off trade for all of us. There are no buyers.''
Today, a sack of coca leaf fetches just $13; locals reckon $22 is breaking even. A year ago, the price was $54. ''People are desperate,'' says Luciano Mancilla, mayor of nearby Palmapampa. ''The entire economy of the valley depends on the coca trade.''
APURIMAC was once among Peru's most fertile agricultural valleys. In 1979, it was the country's third most important producer of high-quality coffee. By 1993, coca had taken over, and coffee production has dropped from 33,000 to 673 sacks. An estimated 25,000 acres of prime cocoa plantations also have been abandoned.
This year, the United Nations Drug Control Program is embarking on a $2.2 million project to help farmers rehabilitate abandoned cocoa and coffee plantations and to diversify into other agricultural activities.
''Forced eradication [of coca fields] has never worked in Peru,'' says a US government official. ''We have to attack the source of cocaine, just as we must attack on the demand side. The problem is that the source base is tens of thousands of farmers. You can't eradicate them, so development is the only alternative.''
Cocaleros agrees. ''In order for us not to plant any more coca, we need decent roads, infrastructure, and electricity,'' says Mr. Barrantes. ''Give us technical assistance for two years and together we can find a healthy solution to the drug problem.''