Bolivians are polarized between presidential candidates offering sharply different visions going into an election Sunday that could fortify South America's tilt to the left and deal a blow to U.S. anti-drug efforts in this Andean nation.

The tight race pits Evo Morales, a leftist coca farmer who would become Bolivia's first Indian president if elected, against Jorge Quiroga, a conservative former president who wants to continue free-market policies and the war on growing coca, which is used to make cocaine.

Morales, 46, who held a slight lead in opinion polls, promised to be Washington's "nightmare" and reverse U.S.-backed efforts to eradicate coca fields.

He counts Cuba's Fidel Castro and Venezuela's Hugo Chavez among his friends and a victory for him would follow wins by leftists in Brazil, Argentina, Venezuela and Uruguay.

The Aymara Indian street activist accused the U.S. Embassy and Bolivia's political establishment of mounting a "dirty war" against him.

"Happily, in Bolivia the people are rebellious in facing up to the empire," Morales said, referring to the United States, in an Associated Press interview. "Despite their accusations, if they want to talk to this 'drug trafficker,' with this 'narcoterrorist,' I don't have any problem. We're always open to dialogue and will always seek diplomacy with any country."

Although a fierce critic of free-market policies that he blames for Bolivia's widespread poverty, Morales moderated his tone as election day approached — assuring the business community that he would protect property rights and fight drug trafficking.

"Morales is an untried political leader. He's certainly someone who can command the street," said Riordan Roett, head of the Latin American studies department at Johns Hopkins University in Baltimore. "Now, can he make the transition from an agitator to an executive?"

Without mentioning Morales by name, Quiroga suggested his rival was making vague promises that wouldn't be delivered on.

"Don't be fooled," Quiroga, 45, a free-market supporter, said Thursday in the wealthy city of Santa Cruz, his power base. "With your support we are going to show that the future of Bolivia is good and prosperous."

Quiroga, who served as president in 2001-02 after then-President Hugo Banzer fell ill, said he would sell Bolivia's vast natural gas reserves at higher prices and improve infrastructure, education and health care in this impoverished nation of 8.5 million.

A wild card in the contest could be the six other candidates. They were expected to win enough votes to deny anyone a majority, and that would push the selection of the president to the newly elected congress, which would choose in mid-January between the two top finishers.

Congress is often pressured, but is not required, to choose the person who receives the most votes. In the five presidential elections since Bolivia returned to democratic rule in 1985, congress has passed over the first-place candidate twice.

Quiroga, an engineer who also has a master's degree in business administration from St. Edward's University in Texas, said he hoped for an outright victory despite Morales' edge in the polls.

"I hope that, beginning Sunday, we will have a government that inspires confidence for the next five years," Quiroga said Saturday as he began a half-day hiking expedition on Huayna Potosi, a snowcapped Andean peak near La Paz that soars to nearly 20,000 feet.

Quiroga insisted that South America's poorest country can only be lifted up by opening its markets, expanding exports and creating jobs.

"The road is long," he said as he joined five fellow climbing enthusiasts in carrying his party banner up the mountain.

Across the country, thousands of police and soldiers spread out across Bolivia's Andean mountains and tropical lowlands to guard polling sites, including remote hamlets reachable only on horseback or in four-wheel-drive vehicles.

Hundreds of foreign election observers were on hand, the largest contingent coming from the Organization of American States.

The acting president, Eduardo Rodriguez, said the groundwork had been laid for a free and fair election.

"What's at stake here is the democratic system and we will safeguard that system on Sunday when we cast ballots," he said at a news conference in La Paz.