Evo Morales, a left-leaning politician and strident critic of US policy, closed his election campaign on Thursday by telling a packed football stadium in the central city of Cochabamba that his Movement to Socialism party was a "political force that has the North Americans trembling".
Bolivians will vote to elect a new leader on Sunday and opinion polls show Morales holding a slight lead over his two rival candidates. He is aiming to become the country's first indigenous president.
Morales is something of a pariah in Washington due to his defence of coca-leaf growing. The crop, which is a key ingredient in producing cocaine, is the target of US anti-drug efforts in the country. Bolivia is the world's third-largest producer of cocaine.
The presidential hopeful has voed that, if elected, he would move to legalise coca. Bolivian Indians chew the shiny green leaf to prevent altitude sickness and brew it in herbal teas.
"We are betting against narco-trafficking, we want 'zero' cocaine but we say no to 'zero' coca," he said.
Washington claims that most of the coca leaf grown in Bolivia is eventually processed into cocaine, but coca farmers say they aim to supply a legal market.
Sean McCormack, the US State Department spokesman, said the Bush administration supported the current Bolivian government's counter-narcotics policy and hoped that the next government would have the same approach.
"We expect whatever government comes next in Bolivia to honour those commitments that they have made to fight the production and transport of illegal drugs," he told a news briefing.
Bolivian coca growers support
Morales's call to legalise the crop
The Cochabamba rally ended months of election campaigning. Morales has travelled throughout Bolivia's mountain hamlets and big cities, hoping to galvanise the country's poor Indian majority that he hopes will sweep him to power.
He has also used his campaign to criticise US policies on free-trade, arguing that they have plunged South America's poorest country deeper into poverty.
Despite his lead in polls, Morales is unlikely to secure the 50% of the vote needed for outright victory and a new president is likely to be chosen by a new Congress, which will also be elected on Sunday, in a vote next month.