* Unexpected spike in deforestation in March, April
* Environmentalists blame anticipation of new law
* Government says committed to lowering deforestation
By Stuart Grudgings
BRASILIA, May 18 (Reuters) - Deforestation in the Brazilian Amazon surged in March and April, the government said on Wednesday, fueling criticism that a proposed law to ease land-use rules may be spurring illegal tree-felling.
Brazil's Environment Minister Izabella Teixeira told reporters the government was creating a "crisis cabinet" to investigate the jump in destruction of the forest, which mostly occurred in the center-west farming state of Mato Grosso.
The area of Amazon forest lost in the two months totaled 229 square miles (593 square km), up 473 percent from the same period a year ago, preliminary satellite data showed.
In the period from last August to April it rose 27 percent, raising the prospect that the closely watched annual deforestation rate will rise this year.
The unexpected leap, at a time of year when deforestation is usually low, comes as Brazil's Congress is locked in a heated debate over a law that would effectively give amnesty to many farmers who have illegally cleared land.
Environmentalists say the bill gives too much weight to the economic interests of the influential farm lobby and will set back recent progress in reducing destruction of the world's largest forest.
"You have 300-400 lawmakers here in Brasilia sending the message that profiting from deforestation will be amnestied, that crime pays," Marcio Astrini, an Amazon campaigner for Greenpeace, told Reuters.
"The only relevant factor is the forest code. It is a gigantic rise."
DELAYED VOTE
Congress delayed a vote on the new forest code last week after days of often acrimonious debate, but it is expected to go ahead next week. A bill that is viewed as rowing back conservation in the Amazon could prove embarrassing for President Dilma Rousseff, who pledged during her campaign last year to maintain Brazil's commitment to protect the Amazon.
Destruction of the forest, which is largely caused by land-clearing for cattle and other farming, is a major source of carbon emissions that contribute to global warming.
The new forest code would reduce the amount of forest farmers must preserve, relax the conservation of hill tops, and provide amnesty from massive fines for past deforestation in Latin America's largest country.
Brazil's farmers say more flexibility on environmental regulations will help them compete on more level footing against other big farming nations such as the United States and Argentina. Brazil is among the world's largest exporters of soy, beef, coffee and other key agricultural commodities.
Teixeira said it was unclear what had caused the deterioration in the huge state of Mato Grosso, which lost half as much forest in April -- 154 square miles (400 square km) -- as it did in the whole of 2010.
The government is determined to ensure deforestation falls in the August-July annual period, she told a news conference.
"The order is to reduce deforestation by July. ... It is a formal promise the government has made. We have to achieve the national plan on climate change," she said.
Deforestation of the Amazon fell to its lowest level on record in the 2009-10 year at 2,509 square miles (6,500 square km), down from a peak of 11,235 square miles (29,100 km) in the mid-1990s. (Additional reporting by Maria Carolina Marcello; editing by Todd Benson and Todd Eastham)
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