But lately they are finding that location may instead be a curse.

The Tikuna community, Mariaçu, lies along a placid stretch of the Solimões River, less than three miles down a reddish-dirt road from Tabatinga, a bustling commercial town.

While seemingly tranquil, the area has become a magnet for drug traffickers who roam the borders here with Colombia and Peru.

Some Indians are accepting cash to work as drug mules, using their knowledge of the rivers and dense rain forest to transport cocaine into Brazil’s growing market, local officials say. And a growing number of young Tikunas are succumbing to drug and alcohol abuse, which Indian leaders blame for some 30 adolescent suicides over the past five years.

For the Tikunas, these traumas represent the latest threat in a fight for tribal survival. With high unemployment and new challenges to its subsistence livelihood, the community is struggling to keep young people from losing themselves in the vices of the white man’s world and from destroying what is left of traditional Tikuna culture.

Like other Indian communities tucked close to growing urban areas, Tikunas are tempted by the consumerism on display and frustrated that it is beyond their means. To the youth especially, alcohol, drugs and drug money seem to offer a way out. They have also unleashed a surge of violence and disobedience.

Alarmed by these trends, Mariaçu’s two chiefs recently made an unusual and desperate appeal for help: they asked the Brazilian police, who generally do not have jurisdiction in Indian towns, to enter their community and crack down on traffickers and substance abusers, even if that would mean putting the Indians at the mercy of Brazilian laws.

“We want government officials to help us save our children, so they don’t take part in these ruinous practices,” said Oswaldo Honorato Mendes, a deep-voiced Mariaçu chief. “Every day the situation gets worse. The younger generation does not obey. They do not show respect for our authority as chiefs. They need to learn respect.”

Respect and obedience to the chiefs are the pillars of tribal law, which usually holds sway in Indian communities but has proved insufficient to cope with new challenges.

The tribal leaders reached a breaking point in early October when Ildo Mariano, 18, hanged himself while his parents were sleeping inside their tiny wood home. For months, he had been drinking and possibly doing drugs with friends who lived in Tabatinga, said his father, Alfredo Mariano.

“He would arrive from class at night and hit the books, and then his friends would pick him up and take him to I don’t know where,” Mr. Mariano said one recent afternoon, as he sat outside on a wood bench while a few feet away his wife boiled pupunha palm tree fruit.

Four days after Ildo’s suicide, the chiefs summoned officials from the federal, civil and military police in Tabatinga to a meeting in Mariaçu, where some 5,200 Tikunas live. They pleaded for the police to do more to control drug traffickers and arrest lawbreakers in their communities. The police officials listened politely but walked away unconvinced they could help.

“It is a desperate request, but not one that we can legally respond to,” said Sergio Fontes, the superintendent of the federal police in the northern city of Manaus, which oversees Tabatinga. “The chiefs want to resolve a social problem with the police, and that is wrong.”

The police generally may not enter an Indian community to carry out investigations, and Indians generally enjoy immunity from Brazilian laws, Mr. Fontes said. In addition, Brazil treats drug users as victims who require treatment, not as criminals. They are usually sentenced to receiving drug-addiction treatment and performing community service in lieu of serving prison time.

And while drugs and alcohol are strictly illegal in Mariaçu, store shelves in Tabatinga are lined with liquor of all kinds. The Tikunas also speak of a white paste, which most think is a form of cocaine, that their youth are mixing with alcoholic beverages.

The Tikunas, who have lived in the region for centuries and migrated to this area in the early 1840s, have traditionally fished and planted bananas and cassava. According to legend, their god, Yoi, fished them from a tributary of the Solimões.

The borders with Peru and Colombia traditionally meant little to them. Leticia, Colombia’s southernmost town, is less than a 20-minute minibus ride away.

They remained largely isolated until the 1940s, when Brazil’s Indian Protection Service, now the Fundação Nacional do Índio, or Funai, created an office for Indian affairs here, making the town a sort of regional capital.

What has happened in Mariaçu “is not the result of any abandonment of Tikuna culture,” said João Pacheco de Oliveira, a professor of anthropology at the National Museum. Rather, he said, history and non-Indian culture have reshaped the world around the Tikunas.

Tabatinga, once a small military town, began growing rapidly as a border trading center in the 1980s and is now home to some 48,000 people. Tikunas began participating in Tabatinga politics in the 1990s, served as military reservists and sent their children to public schools here.

But the region has also been a way station for drug traffickers since the 1970s. The Colombian government’s recent crackdown on narco-guerillas has driven more drug shipments into Brazilian territory, said Mr. Fontes, the police superintendent. The federal police in Manaus have seized more than two tons of cocaine this year, about 1,700 pounds in November alone.

“There has been an escalation of violence in the region of High Solimões, of drug-trafficking gangs, with an astonishing number of killings, and the majority of these gangs are in Brazilian territory,” Mr. Fontes said.

The lack of jobs is proving stifling. A decade ago the fish in the river began to decline.

With Mariaçu’s growing population and stagnant official boundaries there is little room to expand cultivation areas, or to create open spaces for children to play in.

Luz Marina Mendes, a sister of Chief Mendes, said she nearly lost her 19-year-old son, Donizete, twice last year when he tried to kill himself during drug-induced stupors. She walked in on him taking drugs last year, finding a whitish paste that her niece later told her was a drug.

One day Donizete stumbled through the family’s front door in a violent rage, his arm bleeding from a deep, self-inflicted gash. Another day, Ms. Mendes said, she saved him when she found him trying to hang himself.

He later joined the army reserves and cleaned up while living on the base in Tabatinga, she said.

“Virgin Mary, I went through such a rough time with him,” she said, her eyes welling up at the memory. “I struggled so much.”

But reaching for outside help is a thorny issue.

While Indians who have not been exposed to outside culture cannot be prosecuted at all under Brazilian law, so-called acculturated Indians, like the Tikuna, can be under certain circumstances, said Davi Cecílio, head of the Tabatinga office of Funai.

Even so, an acculturated Indian “cannot be imprisoned for the same time as a white man,” he said.

At Tabatinga’s local jail, a half-dozen Indians were recently being detained, suspected of acting as drug mules. Drug traffickers approach Indians because they often do not understand that the substances they are being asked to carry are illegal, said Lt. Francisco Garcia, who runs the jail. The Indians probably suspect that what they are being asked to do is not quite right but often do not fully grasp the grave prison sentences they could suffer in the white man’s world.

And the lure of easy money is tough to resist. Most Tikunas in Mariaçu earn little more than Brazil’s minimum wage of $168 a month. In the jail, Max Tello, a 20-year-old Kokama Indian, another tribe in the western Amazon, said he had accepted $404 in January to take a bag of cocaine up the river, when he was working on a riverboat.

Queliane Gomes, 23, who is part Tikuna and part Kokama, and also in jail, said she was paid more than 12 times as much as what she earned as a housekeeper in Tabatinga to transport a bag of a white substance that, she said, she later learned was cocaine.

While she realizes what she did was illegal, she said Indians should be held to a different standard.

“The law of the white men is the law of the white men, and our law has to take precedence, because our people didn’t get here because of the whites,” Ms. Gomes said. “If we don’t fight for our rights, our ethnicity will cease to exist.”

Portuguese is slowly eroding the importance of the Tikunas language in Mariaçu. Younger Tikunas are less and less interested in fishing for a living or in carrying on the artisan traditions of their elders, residents said. The younger Tikunas “want to have a motorcycle like the whites in town do, to dance to their music, to participate in the regular life of the whites in Tabatinga,” said Joel Santos de Lima, Tabatinga’s mayor.

That lifestyle has brought violence that seems almost inescapable some days, the chiefs said.

“The police are the security of Brazil, and they aren’t doing anything,” Chief Mendes said. “It is their responsibility. It is what they are paid to do.”

But with the police rejecting the Indians’ plea, for now, at least, the Tikunas will have to find ways to cope with their own social problems and the swirling new influences.

“The Tikunas are between two worlds,” Mr. Fontes said, “and I don’t know which one is worse.”