XINGU NATIONAL PARK, Brazil — Naked children are leaping from mango trees and tumbling into the mild water of the Xingu River without a care.
But up by the grass-roofed long houses, the village elders fret that their way of life may soon end.
"We're worried for our children and grandchildren," said Rea, a Kayabi Indian woman. "Our Xingu is an island, and if the white man enters with his machines, he'll break it all down in no time."
Xingu is Brazil's oldest and probably most successful Indian reservation -- 10,800 square miles of pristine rainforest where 14 tribes live much as their people have for thousands of years.
The reserve was established in 1961, just a few years after many tribes in the area had their first contact with white civilization. It sat in the middle of a vast undeveloped stretch in the state of Mato Grosso -- or "thick forest" in English. Today, it is surrounded by fields and pasture in the center of Brazil's fastest-developing agricultural region.
The Indians, whose numbers have nearly doubled to about 5,000 since 1961, say they are feeling the pressure.
"In 20 years, there won't be enough land for all of us. If you look at the park, it's just a triangle with a little rectangle on top," said Awata, the schoolteacher at Capivara, one of several Kayabi villages that line the river.
In the villages, life goes on much as it always has, but there are signs of the encroachment of civilization all around.
Shiny metal faucets are now a fixture in most villages, thanks to a well-digging project that aims to protect the Indians from polluted headwaters outside the park. Once-crystalline rivers are muddied from erosion from farming and logging upriver.
"We can no longer fish with bows and arrows, so we need to buy fish hooks from the white man," said Mairawe Kayabi, president of the Xingu Indian Land Assn., who like many Indians uses his tribe's name as a last name.
The sound of Indians stomping and chanting is still heard in the villages, but now it is as likely to emerge from a cheap tape recorder as from a live ceremony.
In Ngojhwere village, the cooking grill is a bicycle wheel with its spokes hammered down. Three metal car wheels turned on their sides raise the grill over the wood fire on the dirt floor.
Breakfast is piraucu, a freshly caught river fish. The Indians stew it in water and, when it's ready, wrap it in pieces of a big gummy manioc pancake called beiju, with hot pepper and store-bought salt for seasoning.
Women now use steel pots instead of clay to fetch water and cook. Satellite dishes sit outside many long houses, feeding a handful of Brazilian channels to generator-powered televisions.
"All the stuff on the television puts stuff in the young people's heads," Mairawe said. "They are attracted to whatever comes from outside. This is a cause for a lot of disagreement among the leadership."
For ceremonies, the Indians still strip naked and paint their bodies with red powder from ground urucum seeds and the black ink of the jenipapo fruit. But most days, they wear Western clothing -- the women preferring long, cotton dresses, the men shorts and T-shirts.
Kuiussi, the Suya Indians' chief, warns visitors not to take pictures of Indians wearing Western clothes.
"If people see the pictures, they'll say we're not Indians -- that we're mixed [race], and that's not true," he said. "We are all Indians here."
While Kuiussi worries about outside influences, his son, Wetanti, 25, sees no problem keeping a foot in both worlds. He displays a small album that begins with photos of him naked, painted and feathered, and ends with him looking disco-ready in white slacks, a black T-shirt and wraparound sunglasses.
The Suya had their first contact with white men in 1959. Today, the village sits on the edge of the Xingu reservation -- face to face with white civilization.
"Right now, we have to fight to maintain our traditions. The world won't be the same for our children and grandchildren, so we have to hold on to what we have as long as we can," Kuiussi said. "Maybe in the future, they'll want to farm or do something with the land to make money, but not in my lifetime."
The park owes its existence to the Villas Boas brothers. During a 1940s' government expedition to Brazil's hinterlands, the pioneering Indian defenders saw the devastating effect contact with white civilization was having on Indians and their culture.
The brothers lobbied the government to set aside land for the reservation, then persuaded 14 tribes to move into it. At the time, wildcat miners, loggers and farmers were just starting to make their way into the region.
"We taught them [the Indians] if they wanted to survive, if they wanted their children to survive, not to let anyone in. We told them if anyone came to fight them," Orlando Villas Boas, who died last year, said in 1998.