He came to office vowing to be a standard bearer for the dispossessed and excluded of one of South America's poorest nations. "The people are finally in power," Bolivia's first indigenous president, Evo Morales, declared after his historic 2005 election victory.

But, nearly six years on, much of that hope has turned to recrimination as one-time supporters question Morales's true commitment and fears grow that social and environmental issues are taking a back seat to economic growth.

This week, more than 1,000 protesters are expected to arrive in Bolivia's main city, La Paz, to rally against plans for a controversial Amazon road through indigenous lands and voice concern that Morales, an Aymara Indian, is turning his back on the indigenous cause.

"Although Evo is of indigenous descent and was a peasant, he has not been willing to come to [meet us on] the march despite the fact we have been marching for more than 50 days," Rodolfo Lopez, one of the protest's leaders, said.

The march to La Paz began on 15 August, with protesters hoping to highlight a 185-mile road through Bolivia's Isiboro Sécure National Park and Indigenous Territory (Tipnis). Officials say the road will bring much-needed economic development but campaigners fear it will trigger environmental and social chaos, attracting oil and gas companies, illegal loggers and coca growers.

"Nobody is against progress. As indigenous people, we are clear about that," Lopez said. "But I think that as indigenous people we need to defend the natural resources that are benefiting not only the indigenous people but everyone in the world."

Late last month, Morales announced a temporary suspension of construction work, after police clashes with protesters that prompted widespread criticism from human rights groups and politicians, even within Morales's own party.

"It seems a contradiction that an indigenous president rejects the rights of indigenous peoples, and that a president who talks across the world in defence of Mother Earth is now pushing for the construction of a road that will harm the environment," said Franklin Pareja, a political scientist from the Universidad Mayor de San Andrés in La Paz.

Morales, who once described himself as "the candidate of those despised in Bolivian history, the candidate of the most disdained, discriminated against", was re-elected for a second five-year term in 2009 with 64% of the vote. But the government's handling of the protests have soured relations with social movements and his popularity has dipped. Last month, a poll of voters found support for Morales had fallen from 44% to 37%, while 51% now actively disapproved of Morales's government.

Pareja cautioned against writing Morales off but warned that a poor showing for Morales's Movement Towards Socialism (Mas) party in Sunday's judicial elections could trigger a political crisis.

"[The road dispute] has an effect on the credibility of the current government and of course undermines the image of the president who is no longer seen as a defender of the environment or as a defender of indigenous rights," Pareja said. "But despite that, I think that it is premature to think that this is going to weaken the government too much. The current government and President Morales still have a lot of power."

On Monday, flag-waving protesters had ventured within 80 miles of La Paz, their final destination, with no sign of either side backing down.

"There will be blood if they [the government] cut across the indigenous park," Adolfo Chavez, another protest leader, said. "As soon as tractors start building section 2 [of the highway, through the park], they will see the full strength of the indigenous people. We will take steps to defend ourselves."