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Brazilian President Dilma Rousseff used a line-item veto Friday to send back parts of a congressional bill that loosened the nation's benchmark law protecting the Amazon rainforest — a veto the government said would prevent increased deforestation.

Environmentalists were not satisfied because they had called for a veto of the entire bill, known as the Forest Code, saying any weakening of the law would put the world's largest rainforest at risk. Government officials said the partial veto went far enough to keep Brazil on track in its efforts to quell the destruction of the Amazon and other biomes.

"It's the code of those who believe it's possible to produce food and preserve the environment," Agriculture Minister Jorge Ribeiro Mendes told reporters.

Mendes and other officials said the government made 12 vetos and 32 other alterations to the bill, including a requirement for large landowners to reforest land they had illegally cleared, with less stringent requirements the smaller the area involved. Rousseff long indicated she wanted a bill that was less rigorous for smaller, poor farmers and ranchers in the Amazon and elsewhere.

"The big (farmers) have vast extensions of land and have the means to recover all the areas of permanent preservation," Teixeira said.

The bill now goes back to Congress, and legislators have 30 days to override Rousseff's changes with a simple majority, which is considered unlikely.

The Amazon rainforest is considered one of the world's most important natural defenses against global warming because of its capacity to absorb huge amounts of carbon dioxide.

About 75 percent of Brazil's emissions come from rainforest clearing, as vegetation burns and felled trees rot. That releases an estimated 400 million tons of carbon dioxide into the atmosphere every year, making Brazil at least the sixth-biggest emitter of the gas.

The bill revising the Forest Code passed Congress last month after more than a decade of efforts by Brazil's powerful agricultural lobby to make changes to what has been one of the world's toughest environmental laws, at least on paper. The Brazilian government until recently rarely enforced the measure, and authorities are still stymied by a lack of resources as they to police a swath of rainforest the size of the United States west of the Mississippi River.

Environmentalists said changes to the law were disastrous, as they "send a highly negative signal that will lead to more deforestation and undermine deforestation control measures," said Kenzo Juca Ferreira, with the WWF in Brasilia.

The bill as Congress passed it allowed smaller farmers and ranchers to work land closer to riverbanks and on hilltops, which environmental activists say will lead to increased deforestation. Those who support the bill, however, said it gives long-needed help to smaller Brazilian farmers forced off the land by the strong environmental restrictions on how they can work.

The bill had big support in both houses of congress. The Senate version of the bill provided more protections to sensitive environmental areas, but the bill that arrived before Rousseff was that passed by the House, which further loosened the law and was viewed by the president as not tough enough to combat deforestation.

Backers of the bill said recent drops in deforestation indicate pragmatic changes to the law could be made without leading to new destruction, by more effectively enforcing environmental protections that until somewhat recently were virtually ignored by Brazil's government.

About 20 percent of Brazil's Amazon rainforest has been destroyed. But beginning in 2008, the government stepped up enforcement, using satellite images to track the destruction and send environmental police into areas where deforestation was happening at its quickest pace. Amazon deforestation slowed and hit its lowest recorded level from August 2010 through July 2011, when just 2,410 square miles (6,240 square kilometers) were felled.

However, there are just 1,400 federal environmental police to cover the vast and often impenetrable Amazon along with the rest of Brazil, leading environmentalists to worry that further drops in the destruction may be unlikely — and might even return to increasing because the new bill loosens restrictions.

Opponents of the bill also argue that while government enforcement did help slow deforestation, temporary economic factors also played a role — that demand for the cattle, soy, timber and iron ore produced in the Amazon fell in the United States and Europe as the global financial crisis took hold. It's feared the appetite for those goods will increase and lead to a resumption in destruction once the world economy recovers.

The most contentious part of the bill passed by Congress was that it scrapped most protections for riverbanks, including maintaining strips of forest 30 yards (meters) to 100 yards (meters) deep along waterways. The version sent to Rousseff mandated only that small rivers maintain 15 yards (meters) of forest along their banks, which are sensitive to rapid erosion that can then reduce water quality, promote flooding and affect the plants and animals that use the rivers to survive.

Teixeira's indication that Rousseff was returning the bill back to what the Senate approved indicates that protections for riverbanks would be reinstated, though to what extent won't be known until Monday.

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Bradley Brooks on Twitter: http://twitter.com/bradleybrooks

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Associated Press writers Marco Sibaja in Brasilia and Stan Lehman in Sao Paulo contributed to this report.