COCA, ECUADOR -- A band of Amazonian Indians sent a clear message last month when they sacrificed a Roman Catholic bishop and a nun who had come to their jungle village to bring them the word of God.

The clerics were left pinned to the ground by 21 heavy wooden spears. Their bodies bore 109 other spear wounds. Many of the wounds had been stuffed with leaves to stanch the flow of blood -- and prolong the victims' suffering.

To emphasize the point, the Indians erected a pole with a bone tied to its top next to the mutilated bodies -- a warning that any white man who ventured into their territory would meet the same fate.

There is war in this corner of the Amazon jungle.

The two Catholic clergy -- Bishop Alejandro Lavaca, the 67-year-old head of this sprawling jungle region, and Sister Ines Arango, 50 -- were but the latest victims of a brutal cultural struggle that has pitted a dwindling band of primitive warriors against civilization's formidable army of oil companies, settlers and Christian missionaries.

And as civilization's forces grow, the violence is likely to grow with it.

On one side are about 15 U.S. and European oil firms, invited by the Ecuadorean government to help exploit the riches of the nation's Amazon region. In the four years since the companies began exploring 6 million acres of once-virgin jungles, the population has soared. There were about 3,000 people living in the Amazon in the early 1970s. Now there are more than 100,000.

Bulldozers and chain saws plow roads through the thick forest. Throughout the region, exploration teams set off dynamite charges as part of their search for precious petroleum.

On the other side are the Waorani Indians (pronounced hwa-RAH-nee), many of whom have never had direct contact with outsiders. They still walk naked. Their bodies have no immunity to such scourges as flu, measles and chicken pox. They live off what they hunt.

And they worry that the dynamite is frightening away monkeys, their main source of food.

"They don't like to see the jungle shaken by noises," said Camilo Pauchi Padilla, 24, a member of a Waorani tribe that lives near what he describes as the "free" Waoranis. "They think they are going to run out of food. They think they are being invaded."

Increasingly, the Indians -- and not just the uncivilized ones -- are fighting back. In one incident Aug. 7, an Indian was killed and a settler wounded in a battle over land rights at the outpost of Paroto Yaco.

"We are defending our home, the land on which we live," said Alberto Tanguila, an Indian leader in Coca. "We will defend it with whatever it takes . . . be it with our bare hands, sticks, stones or other weapons."

It could be a long and bloody struggle. The Waoranis are also known as Aucas -- "killers."

There is no direct way to reach this area these days. An earthquake in March destroyed the roads and bridges leading to Coca, the last town on the edge of the jungle. A trip to reach the Aucas (pronounced ah-OO-kas) means a military flight to the outpost of Lago Agrio, a canoe ride across the Aguarico River and an arduous, two-hour drive south.

The hilly jungle road leading to Coca is virtually covered by the forest's vegetation. Plantain and coconut trees rise like towers from thick walls of plants in various shades of green. On both sides of the road, isolated wooden houses are built on poles to prevent them from being washed away by torrential tropical rains.

Men with machetes and rifles walk along the road under the scorching sun. The driver of an improvised taxi points out a 12-foot boa along the road.

It is here that the semicivilized Indians tell a visitor of the Auca tribe known as the Red Feet, which killed the bishop and the nun.

Red Feet women are naked. Red Feet men wear little more than a string around their waists. They paint their legs and bodies with red dye made from seeds of the annatto tree.

Because the food in the jungle is often scarce and the thin Amazonian soil is not good for successive crops of yucca, the Red Feet move about every two years. They generally live in small communities of up to 40 people, separated by many miles from other settlements.

The Red Feet kill their first-born daughters in a ritual drowning that anthropologists say may be an unconscious form of population control. The elderly, when they can no longer move with the tribe, ask to be stoned to death or buried alive. Among the Aucas, the fear of death is overshadowed by an inbred feeling that survival of the tribe comes ahead of any individual's wishes.

Other Indians fear the Red Feet. The killers have been known to attack other tribes and kidnap women.

The Red Feet's current war began in 1956, when they speared to death five U.S. evangelists who ventured into their territory. In the last 10 years, there have been at least a dozen deadly attacks on workers of oil, lumber and palm companies. One victim was the cook of an oil firm who inadvertently picked yucca plants from a small plantation that the Red Feet had left in the jungle. The man died that night in a spear attack.

Bishop Lavaca worried about the deaths. As oil firms advanced farther into the jungle, there would surely be more violence.

In a Feb. 11 letter to the secretary general of the Quito-based Ecuadoran Bishops Conference, Lavaca sent a map of the latest oil exploration roads in the Amazon "so that you can see how the jungle is being crisscrossed in all directions by these tracks."

At his Capuchin Brothers mission in Coca, Lavaca and the 17 missionaries under his direction began to make plans to locate and evangelize the Red Feet before new attacks on oil exploration teams took place.

In March and April this year, Lavaca, who for two years had a contract with Ecuador's State Petroleum Corp. (known by its Spanish initials as CEPE) to contact the distant tribe, made eight flights to the jungle area where killings by the Red Feet had been reported.

In April, Lavaca spotted from the air two women and four men who seemed to be Red Feet. He took note of their location and returned to the mission to plan his next move. The Spanish-born bishop, who had been living in Ecuador for three decades and had easy access to high-ranking officials, persuaded CEPE to extend his contract, which was about to expire.

At 5 a.m. on July 20, without notifying a small group of scientists camping two miles away from the Red Feet and who were part of a CEPE-church plan to contact the Indians, Lavaca loaded the helicopter with presents and took off to the land of the Red Feet. He was enthusiastic.

"He had been dreaming for a long time of establishing contact with these Indians," said Archbishop Bernardino Echeverria of Guayaquil, who had sat next to Lavaca at a church conference a few weeks earlier. "The euphoria with which he talked about his mission got our attention at the time. He was hoping to conquer this tribe for Christ, as he had done with many others."

At the Red Feet's jungle village, Lavaca began to drop presents from the helicopter. He threw sterilized machetes, cooking pots and packages of salt.

One or two Red Feet made what Lavaca interpreted to be friendly signs. The bishop decided to make his big move. He packed some food rations, told the pilot to come back in two days and, with Sister Arango, descended a rope ladder.

The pilot found their bodies when he returned.

The corpses were left on open ground a few feet away from an Auca straw hut. No one knows exactly what happened before the two died, but anthropologists speculate that the Aucas followed an ancient ritual: after their victims had died in agony, each male member of the tribe stuck one spear through the bodies, deep into the ground.

Bishop Lavaca made several serious mistakes when he decided to climb down the ladder, said social scientists who live in the jungle and who have followed the Aucas for years in preparation of a possible friendly encounter.

Lavaca's first mistake was to approach the Red Feet in a helicopter, which surely intimidated the Indians, said social scientists close to the case.

Second, Lavaca did not notice a red stripe on the roof of one of the Red Feet's straw huts. The sign, much like the stick with a bone tied to its top, is a declaration of war against intruders.

Third and most serious, Lavaca misread the Indians' smiles and hand signs as a declaration of friendliness.

The 21 wooden spears found in the bodies are imposing weapons, each measuring nearly 12 feet and decorated with rope ornaments.

Brother Jesus Elizalde, a Spanish Capuchin friar at Lavaca's mission, could hardly lift one of the heavy shafts when he showed a visitor five of the spears that were pulled from the bishop's body. The spears will be exhibited at the mission, he said.

Another of the giant spears has been shipped to Quito, where it is on display at the headquarters of the Bishops' Conference. A plaque commemorating Lavaca's and Arango's heroism is nearby.

"He has demonstrated that even in our days, it is possible to offer one's life for faith," said the Rev. Antonio Arregui, secretary general of the Conference of Bishops, as he showed the weapon mounted on the wall. "This gives us new energy to pursue his mission. It encourages us to pick up the work where he left it."

Critics of the church's latest actions are shaking their heads. If the bishop committed many mistakes, those who recovered his body and the church officials who are keeping the spears are making much more serious -- and potentially dangerous -- errors, they said.

"Spears are these Indians' most important symbols, just like national flags are ours," said one social scientist who asked not to be identified.

"To have taken away the spears as relics is the biggest offense they could have done to them," the scientist said. "As far as they're concerned, the white man has taken up a challenge."