RIO DE JANEIRO, Oct 1 (Reuters) - In March 2003, three months into her tenure as Brazil's environment minister, Marina Silva gathered a half-dozen aides at the modernist ministry building in Brasilia, the capital.
She told them the new government of President Luiz Inácio Lula da Silva was about to embark on a pharaonic infrastructure project for Brazil's arid Northeast.
The project, a still-ongoing effort to reroute water from one of Brazil's biggest rivers, had previously been opposed by environmentalists, including Silva herself.
Rather than explain how she would thwart the plan, however, the former activist said she would work to make it as sustainable as possible.
"I was shocked," says Marijane Lisboa, a former Greenpeace director and Silva's secretary of environmental quality then. "Instead of fighting, she was merely trying to mitigate."
Lisboa would not be the last person surprised by Silva, a former rubber tapper and maid and now a frontrunner in Brazil's presidential election race.
Once considered a leftist radical, the pioneer of Amazon conservation and icon of the global environmental movement has over the years marched steadily to the political center.
A 56-year-old-mother of four and evangelical Christian, Silva barely trails President Dilma Rousseff in forecasts for an expected runoff three weeks after a first round of voting on Sunday.
She is buoyed by discontent over corruption, political horse-trading, a stagnant economy and poor public services that last year sparked mass protests across Brazil.
But Silva is also a pragmatic, calculating and deal-making politician who defies efforts by rivals to cast her as inexperienced, or worse, erratic.
After moving across three parties in recent years, Silva now represents the second-tier Brazilian Socialist Party and vows to expand popular social welfare programs even as she slashes government spending.
She would pursue renewable energy programs, like biomass and solar power, but promises to keep developing the "one-time harvest" of offshore oil.
"Why does one activity have to come at the expense of another?" she said during a recent interview with Reuters in Rio de Janeiro. "A strong economy is diversified."
Silva's shift outrages some militant former followers and former colleagues in the ruling Workers' Party.
But it attracts disparate others - fellow evangelicals, São Paulo financiers, youth sick of the status quo.
If elected, her biggest struggle could be weaving the sundry strands of support into a manageable harness for Brazil's rambunctious multi-party democracy.
In interviews, more than a dozen of those who know Silva describe a thoughtful politician firm enough to lead but pliant enough to bend when an opposing argument prevails. They say her five years as minister, and political comeback since a high-profile resignation in 2008, show her ability to set priorities, pursue goals and compromise.
"Call her anything but dumb," says Roberto Rodrigues, a former agriculture minister who clashed with Silva in the Lula administration over genetically modified crops and forestry laws. "She knows a militant cannot be president."
Silva's remarkable rise from illness and illiteracy in the rainforest to the Senate and beyond is already political lore. But her evolution from activist to possible president still puzzles many who thought her incapable of the give-and-take needed at the highest levels of politics.
In 2002, Brazilians elected Lula, a fiery former union leader. After naming a market-friendly finance minister, who soothed fears the president would be fiscally reckless, Lula made Silva his second cabinet appointment, garnering praise from conservationists worldwide.
Upon taking office in January 2003, Silva told department heads to plot priorities for the four-year term. The previous administration, of centrist Fernando Henrique Cardoso, had been too busy taming Brazil's volatile economy to pay much attention to environmental issues.
Silva held big meetings and fielded proposals for waste policies, watershed management and parkland.
But she had one overriding concern: soaring deforestation. Loggers and ranchers were pushing so quickly into the Amazon that an area the size of Belgium was being destroyed annually.
Silva proposed setting targets for curbing the rate of deforestation. She told a committee to map out a plan to reach them and rebuffed aides who suggested such targets could doom her politically if unmet.
"I'll deserve political failure if we don't reach them," she said, recalls former forestry secretary João Paulo Capobianco, still one of her closest advisors. "Whatever we do in other areas, deforestation is the measure by which we will be judged."
Some aides complained she paid little mind to anything else.
When it came to rerouting the São Francisco river, she offered sparse resistance, settling for a commitment that long-polluted parts of the river be cleaned up during the project. "If it was outside the Amazon, it was not a priority," says Gilney Viana, secretary for sustainable development then.
Soon, political conflicts intruded on her agenda.
Big meetings gave way to individual discussions with aides able to help her negotiate with the rest of the administration. "She spent more time courting Lula and other ministers than running the ministry," recalls one aide, who asked not to be identified because of continued ties to the government.
The agriculture ministry, a powerful force in one of the world's largest exporters of crops, was particularly problematic.
Early on, it sought to convince Lula that genetically modified soybeans growing in southern Brazil be allowed for sale. So-called "Maradona seeds," smuggled from Argentina, were still illegal in Brazil but farmers planted them anyway.
Silva lobbied against their sale. She also sought to ensure that her ministry control a new government body to regulate genetically modified crops.
She lost on both counts.
Already, environmentalists pushed her to resign in protest.
Instead, she secured a legal change forcing manufacturers to label foods containing genetically modified ingredients. "She knew how to negotiate," says Beto Albuquerque, a former congressman from the state where the soy was planted.
Once an antagonist, Albuquerque is now Silva's running mate.
Meanwhile, Silva progressed against deforestation.
Whereas the ministry had once battled alone, she convinced 12 other federal agencies, from the army to the justice ministry, to help. The science ministry, headed by a promising young politician named Eduardo Campos, ceded government satellites to track clearings.
In 2006, deforestation plunged to half the rate in 2004.
The following year, soaring demand for Brazil's commodity exports was fueling an economic boom. With re-election in sight, a group of ministers convinced Lula to dust off a series of long-proposed infrastructure projects, including hydroelectric dams on Amazon tributaries.
Some ministers, including Rousseff, Lula's chief of staff, pushed for speedy licensing. Silva resisted, angering Rousseff and the large builders who help finance Workers' Party coffers.
When Lula was re-elected, Silva was the last existing minister re-appointed.
In late 2007, gains against deforestation stalled, in part because of speculation on rainforest near proposed infrastructure sites. Silva convinced Lula to double down, introducing measures to block credit for those caught buying or selling goods from illegally cleared woodland.
When farmers complained, Lula considered revoking the measures.
In May 2008, Silva resigned. "I may lose my head," she said, "but I haven't lost my judgment."
Where some saw defeat, supporters saw wile.
"Lula could drop the measures and take the blame when deforestation worsened," says Tasso Azevedo, a forestry engineer who still advises Silva, "or he could keep them and take the credit for improvement."
Lula left them intact. The pace of deforestation during his two terms decreased by 75 percent.
After resigning, Silva quit the Workers' Party and found a brief home with Brazil's Green Party. More importantly, she courted resourceful allies, especially Guilherme Leal, the billionaire behind Natura, a cosmetics empire built on locally-sourced ingredients, many of them from the Amazon.
Leal says he admired Silva's "strategic vision" for a country with the world's largest rainforest and abundant sources of water and clean energy. He also admired her political chops.
"It's in her DNA," Leal says. "She puts the knife between her teeth and goes. Not after power for power's sake, but for the sake of political action."
Leal financed a presidential campaign for Silva in 2010 and joined her ticket as running mate. He also introduced her to an influential group of economists, business people and financiers.
Now an important part of her power base, those people repel some of Silva's former fans.
Leonardo Boff, a prominent theologian and anti-poverty activist who has known Silva since her youth, says she has surrounded herself with "neoliberals" - capitalist types unpopular with some leftists.
Still, Silva surprised. She reaped 20 percent of the vote in 2010, far more than expected.
Green Party leaders were annoyed that a newcomer had eclipsed them so Silva defected and tried to form a new party.
When a court ruled last year that the party did not meet electoral requirements for this election, she turned to another ally: Campos, the former science minister, by now a popular governor and a presidential aspirant himself.
Campos made Silva his vice-presidential candidate. He then died in a plane crash in August and Silva moved to the top of the ticket.
At a recent rally in Rio, Silva denounced "savage marketing" by opponents suggesting she would halt oil exploration in the region. She chastised the Workers' Party, itself the target of scaremongering before it came to power, for painting her as a radical.
"I fought against lies back then," she said. "Now they want to use the same rusty knife against me." (Editing by Todd Benson and Kieran Murray)