And while small farmers like Mr. de Souza are pinning their hopes on the law, many larger-scale land holders say they have sacrificed too much blood and sweat for bureaucrats in Brasília, the capital, to force new rules upon them.

“Everything we have today was built from our own desire to work,” said Jorgiano Alves de Oliveira, 68, who raises cattle and grows cocoa on about 600 acres.

The problem began with the military dictatorship in the 1960s and 1970s, which invited settlers to occupy the Amazon but required them to clear forests to gain access to land and credit.

Image Raimundo Teixeira de Souza held the residents’ card of his stepson who was killed, probably in a land dispute. Credit... André Vieira for The New York Times

Growing criticism of Brazil’s Amazon policies pushed the civilian government of the 1980s to develop laws that, on paper at least, were among the world’s most protective of forests. But with scant presence of authorities to enforce them, the laws did little to stop the widespread grabbing of land.

“This chaos of legal insecurity was the most important basis for the perverse incentives in the Amazon to pillage rather than to preserve or to develop, and constant incitement to violence,” said Roberto Mangabeira Unger, the former minister for strategic affairs who helped develop the new land law.

Under the law, which applies to more than 150 million acres, the government will award plots up to 250 acres free to settlers. Bigger plots will be sold at varying prices, with or without public auctions, depending on their size. Those larger than about 6,000 acres cannot be sold without an explicit act of Congress. So far, settlers have registered about 4 percent of the land singled out under the law, according to government officials.