(Adds Silva letter, comment on successor, paragraphs 5, 9)
By Raymond Colitt
BRASILIA, May 13 (Reuters) - Brazil’s environment minister, hailed as a champion of the green movement but scorned by powerful farming groups, resigned on Tuesday after losing key battles in her efforts to protect the Amazon rain forest.
Marina Silva’s resignation is likely to reinforce the view that President Luiz Inacio Lula da Silva is more concerned with economic development than conservation as a commodities export boom fuels Brazil’s growth.
It could also be a setback for Brazil’s ambitions to become a major voice in global environmental debates.
"Her resignation is a disaster for the Lula administration. If the government had any global credibility in environmental issues, it was because of minister Marina," said Jose Maria Cardoso da Silva, environmental group Conservation International’s vice president for South America.
Silva said in her resignation letter that she stepped down because of the "difficulty she had been having for some time in carrying out the national environment agenda," a presidential spokesman said.
Farming leaders welcomed the resignation of the former rubber tapper and leftist activist.
"I hope the next minister is not as radical as Marina. She was an obstacle to economic development in Brazil," said Rui Prado, head of the agriculture federation of Mato Grosso, a big farming state.
Silva unsuccessfully opposed several infrastructure projects in the rain forest, including two hydroelectric dams and a road that will link the western grain belt with the Amazon River.
Among Silva’s possible successors is Carlos Minc, Rio de Janeiro state’s environment secretary and a founder of the Green Party in Brazil, local media reported. The presidential spokesman could not confirm his appointment.
The soft-spoken Silva has been ill for years with tropical diseases and metal poisoning.
She was frequently at odds with other Cabinet members and Lula, who she felt were more concerned with job growth and conquering foreign markets than with protecting the environment.
Growing global demand for Brazilian commodities such as soybeans has helped accelerate destruction of the world’s largest rain forest, and Silva blamed cattle ranchers and farmers who have pushed deeper into the forest in search of land.
Lula publicly rebuffed her and named Roberto Mangabeira Unger, minister for strategic issues, to oversee the implementation of a government white paper on the Amazon.
At the presentation of the proposal last week, aides of Silva and Lula clashed and publicly accused each other of incompetence.
Silva also lost out to big business interests when the government authorized genetically modified grains and the construction of a third nuclear power plant.
Marcelo Furtado, the campaign director for Greenpeace Brazil, said the resignation was "disastrous" and blamed it on the government’s Amazon policy, pressure to ease environmental regulations on factories and Unger’s appointment.
"Although Lula has adopted the environmental talk, the practice is development at whatever cost," Furtado said.
The Amazon basin covers half of Brazil and holds a fifth of the world’s fresh water, and 15 percent of all plant and animal species on earth.
But illegal logging and mining are rife as well as legally sanctioned felling, and swaths of land the size of U.S. states have been deforested in recent years.
Between August and December 2007, an estimated 2,703 square miles (7,000 square km) were chopped down, equivalent to two-thirds of the total for the previous 12 months.
Silva was an admired figure in the global environmental community and often wore ethnic-style clothing. Born to a humble family in the Amazon state of Acre, she worked as a rubber tapper and a maid before earning a university degree.
She worked closely with renowned activist Chico Mendes supporting local communities against big farmers and loggers until his murder by ranchers in 1988.