Peru has failed to cut its drug output since 2000 despite some $330 million in U.S. aid and Garcia has promised a fresh drive to slash coca output after it jumped some 40 percent in 2005. Peru ranks as the world's No. 2 cocaine producer, after Colombia and ahead of Bolivia.
"The government has been warned. If this repression, this eradication, continues ... we're going to have deaths in our coca regions. ... We are preparing for war," Nancy Obregon, a lawmaker and coca farmers leader, told foreign correspondents.
Coca growers clashed with police in northern Peru this month as the government intensified its eradication efforts, causing dozens of injuries.
The government said crop eradication would continue.
"There'll be no suspensions, we've never considered stopping eradication. We've got a plan and targets to meet," Interior Minister Pilar Mazzetti told a news conference.
Farmers say their crop is sacred and is not part of the narcotics trade, but an ancient leaf with medicinal qualities used by the Incas long before the Spanish conquest.
Obregon, of the Nationalist-UPP party led by opposition leader Ollanta Humala, said coca farmers want an "enlightened" drugs policy that allows for a crackdown on cocaine traffickers mixed with state promotion of coca for health and medicinal uses to create a legal coca market.
"How can it be that Peru produces 190 tonnes of cocaine every year and the police only catch 11 tonnes? Yes, we need to stop the trafficking, but they can't take away the only crop farmers have to live on," said Obregon's aide Ricardo Soberon.
Small amounts of coca are grown legally in Peru for chewing as a stimulant and for tea to alleviate altitude sickness. Peru's government says only 10 percent of production goes toward such ends and the remainder is turned into cocaine.
Coca growers reject that figure and say the leaf's high calcium content makes it a key part of the Andean diet. (Additional reporting by Maria Luisa Palomino)