NOVO PROGRESSO, Brazil — As the fires rage, the helicopters of the environmental police at this outpost in the Brazilian Amazon cannot even take off some mornings because the sky is so thick with smoke. The plumes, sent up by the burning of the forest to clear land for cattle grazing, have grown so vast this year that astronauts have photographed them from the International Space Station.

From the podium at the United Nations to declarations on the campaign trail, President Dilma Rousseff is celebrating Brazil’s protection of the Amazon. But satellite data released last month shows that Brazil’s annual deforestation rate in the Amazon has climbed again after years of declines, rising 29 percent, leaving her vulnerable to attacks in this nation’s acrimonious presidential race. The vote is on Sunday.

“The mantra in Brasília is that they have deforestation under control, but the evidence on the ground shows this is not true,” said Philip M. Fearnside, a prominent researcher at the National Institute for Amazon Research in Manaus, the Amazon’s largest city.

Beyond alarming scientists, who note the importance of the vast rain forest to the world’s climate and biodiversity, the sparring over the Amazon symbolizes clashing visions of Brazil’s future. Both Ms. Rousseff and her top rival, Marina Silva, an environmental leader, say they want forest conservation, but the president’s model seeks economic growth by tapping into the Amazon’s natural resources, including huge mining projects and dams.