When members of the Shalabi family went out recently to harvest their olives, they discovered that a few dozen trees had been chopped down, their branches hacked by vandals. In other groves belonging to this Palestinian village, there were scores of dead trees that had apparently been poisoned, with holes drilled in their trunks.

The groves are near Adei Ad, an unauthorized Jewish settlement outpost, and villagers, citing past incidents of assaults and harassment, pointed an accusing finger at the settlers.

"You work hard for years to tend the tree, like raising a child, and when you see it destroyed, the feeling cannot be described," Nahil Shalabi, a family member, said as she surveyed the damage. "No one stops them," she added, referring to the vandals.

The olive harvest is an annual ritual in the rocky hills of the West Bank. Families take to the groves to work and picnic together, climbing ladders to pick the hard green or black fruit, a traditional staple of the Palestinian economy, or knocking it off with sticks onto tarps spread under the trees.

But the harvest is also a time of heightened tension between Palestinians and militant Jewish settlers, with some of the olive groves near the settlements becoming a front line in the struggle over land in the West Bank.

Talk of a possible renewal of a building freeze in the settlements to save stalled talks with the Palestinians has further charged the atmosphere, posing a challenge to Israeli security forces posted to secure the harvest.

In groves of several villages near Havat Gilad, an outpost of militant settlers southwest of Nablus, Palestinians out to harvest their olives have discovered tracts of trees picked clean, their fruit taken by vandals. In other locations, villagers have reported dozens of trees cut down, and hundreds more grazed by settlers' goats and stripped of leaves and fruit.

Following repeated assaults on harvesters in recent years, and after an Israeli Supreme Court ruling required the army to ensure that "every last olive" is picked, military authorities in the West Bank have developed an elaborate plan to protect Palestinians working in groves near Jewish settlements and outposts. Dates and locations of work are coordinated with villagers, and border police and soldiers are posted in the areas to deter settlers and guard the harvesters.

Although access has improved at olive groves where settlers have kept Palestinians out, incidents of vandalism and theft persist.

Rabbi Arik Ascherman, director of Rabbis for Human Rights, an Israeli group that assists the Palestinian farmers, said the security forces were doing a better job of guarding harvesters but were failing to protect property and bring vandals to justice, a task which required more resources.

"As long as Israel is maintaining an occupation, it has got to bear the cost," Ascherman said. "It is legally obligated to protect the Palestinians, but the record of the security forces has not been adequate."

Lt. Amir Koren, spokesman for the Civil Administration, the Israeli military government in the West Bank, said that extensive resources and manpower had been devoted to securing the harvest, but "you can't have a soldier posted at every tree." He said that cases of vandalism and theft were a matter for the police.

Micky Rosenfeld, a police spokesman, said that the damages and theft of olives were "not a phenomenon" that was widespread and that there had been similar complaints by settlers reporting property damage by Palestinians. He said that investigations had been opened and several suspects questioned and released, but that no one had been charged.

Yesh Din, an Israeli advocacy group that has tracked police investigations of damage to Palestinian trees, said that in a review it conducted last year, not a single probe had led to an indictment. Many cases have been closed in recent years on the grounds that "the offender is unknown," according to data compiled by the group.

In the groves of Turmus Ayya, Mahmoud Hazama, a local farmer, told an Israeli police officer about the damage to the village's trees and pleaded for access to a plot of land that had been fenced off and cultivated by settlers. The officer told Hazama to file a complaint at an Israeli police station in the area. "You say settlers, but you have to specify person X, Y or Z," the officer said.

Avigdor Shatz, the security chief of the Jewish settlements in the area, drove by in his jeep. "The police are weak, in all directions," he said, referring to responses to complaints by settlers and Palestinians. "There are extremist elements on both sides. We condemn any damage. Everyone should be able to harvest their olives."

A spokeswoman for the settlers' regional council, Tamara Asraf, said that in the vast majority of locations, even inside the limits of settlements, Palestinians were picking their olives without incident in coordination with the security forces.

Down a dirt road, Ratib Naasan, from the neighboring village of Mughayer, was supervising work at his olive groves, not far from the settlement outpost. He said that a few days earlier, he had spotted settlers picking his olives, and after he called the police, the settlers fled, leaving behind three large sacks full of harvested fruit.

Naasan said that the settlers wanted more than just olives. "They want to evict people and take the land," he said. "All of it."