BRASÍLIA—Brazil’s government, under fire from Western governments over deforestation in the Amazon, will ask developed countries to help finance efforts to preserve rainforest and promote sustainable economic activities during a climate-change conference in December.

Environment Minister Ricardo Salles on Wednesday said his country will call on rich nations during the two-day United Nations conference, known as COP25, to provide $100 billion a year to help Brazil and other developing countries preserve their natural resources,...