BRASILIA, Brazil _ The future of Brazil's traditional Indian cultures was under challenge on Wednesday as Brazil's Supreme Court began hearing arguments on whether to break up a vast Amazon reserve.

The dispute over the 4.2 million-acre (1.7 million-hectare) Raposa Serra do Sol reservation pits about 18,000 Amazon Indians against a handful of large-scale rice farmers who have violently fought efforts to remove them.

Indian-rights advocates say a ruling against the reservation could set a precedent that would eventually destroy policies that grant Indians land and autonomy to maintain their traditional cultures.

Politicians from Roraima state, however, say leaving the entire reservation in Indian hands is a threat to national security and strangles economic growth in the sparsely populated state.

State lawyer Luiz Valdemar Albrecht urged the justices to cut the reserve into pieces so the rice farmers can stay alongside 18,000 Indians from the Macuxi, Ingarico, Patamona, Wapixana and Taurpeng tribes.

He argued the anthropological study saying the tribes traditionally inhabited the land was a shoddy "cut and paste job."

Attorney Joenia Batista de Carvalho, a Wapixana tribe member representing the Indians, said the reservation resulted from a decades-long effort to right wrongs that began five centuries ago during colonization by the Portuguese.

While Brazil's 1988 Constitution mandated the demarcation of Indian lands within five years, the Raposa Serra do Sol reserve wasn't created until 2005, and the government still hasn't enforced its borders.

Indians hold about 11 percent of Brazil as a whole and 22 percent of the land in the Amazon, an area increasingly sought by farmers producing some of Brazil's biggest exports _ beef and soy.

Fiona Watson, a coordinator with London-based Survival International, said Indian lands are coveted precisely because traditional land management schemes keep them productive.

"Farmers can use these lands because of the way Indians have traditionally used the land in harmony with the environment," Watson said.

The Supreme Court agreed to hear the case after a federal attempt to evict the rice farmers set off protests in which settlers burned bridges and hurled Molotov cocktails at authorities.

The court said it needed to resolve a situation that could turn into a "veritable civil war."

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Associated Press writer Michael Astor contributed to this report from Rio de Janeiro.