Palestinians from villages like this one in the West Bank governorate of Ramallah still remember when the olive harvest was a joyous occasion, with whole families out for days in the fall sunshine, gathering the year’s crop and picnicking under the trees.

“We considered it like a wedding,” said Hussein Said Hussein Abu Aliya, 68.

But when Mr. Abu Aliya and his family from the neighboring village of Al-Mughayer — 36 of them in all, including grandchildren — drove out to their land this week in a snaking convoy of cars and pickup trucks with others from Turmus Aya, they found scores of their trees on the rocky slopes in various stages of decay, recently poisoned, they said, by Jewish settlers from an illegal Israeli outpost on top of the hill.

Branches drooped, the once lush, silver-green leaves were turning brown and the few olives still clinging on, which should have been plump and green or purple by harvest time, were shriveled and black. Dozens of trees nearby that Mr. Abu Aliya contended were similarly poisoned with chemicals last year stood like spindly skeletons, gray and completely bare.

Religious Jewish settlers consider the West Bank, which Israel captured from Jordan in the 1967 war, as their biblical birthright. For the 2.5 million Palestinians of the West Bank, it constitutes the heartland of a future independent state. While the Americans and Palestinians wrangle with the Israeli government over continued Israeli construction in the West Bank settlements — an issue that has stalled the embryonic peace talks — the competition for control of each acre of land here is being played out day by day.

And the olive tree, an ancient symbol of peace and plenty that has also long been a Palestinian emblem of steadfastness and commitment to the land, has increasingly become a symbol of local, almost intimate, struggle and strife.

Husniya al-Araj, 60, said she was born in a cave nearby, in an orchard of olive and almond trees. But when she reached her family lands this week, she cried out in shock. She pointed to a newly plowed field in front of her that she said was part of her family property, but that seemed to have been taken over by the settlers. It was now surrounded by a shiny new barbed-wire fence and planted with young vines.

Mahmud Ahmad Hazama, a relative who takes care of the Araj family property, said the barbed-wire fence went up in July. Folded in his wallet was a handwritten record of every change and every complaint Mr. Hazama had made to the Israeli Army and police since 1995.

“They ask me for documents,” he said. “We have all of them. The last thing they asked for was a topographic map.” He said he had received no answers so far.

Micky Rosenfeld, an Israeli police spokesman, said the police were aware of the problems. Every complaint is investigated, he says, but sometimes the culprits turn out not to be settlers, and sometimes there is not enough evidence to know. In some cases, the complaints do lead to arrests of settlers, he says.

Tamar Asraf, spokeswoman for the Binyamin Council, which represents the settlers in this region, said that for the most part the olive harvest passes peacefully, but that there were Palestinians and settlers who cause damage to one another. “We condemn them both,” she said.

Mr. Hazama’s relatives, like many other families, found their olive trees intact but empty of fruit. They argued that the olives must have been stolen by settlers, though they had no proof.

In other villages to the north, like Yanoun, Jit and Imatin, olives were stolen from hundreds of trees in the past few days, according to Rabbis for Human Rights, an Israeli organization that helps Palestinians farm lands in trouble spots year-round.

This was the first time the villagers of Turmus Aya and Al-Mughayer had been able to have access to their lands in six months. To do so, they need permission and protection from the Israeli Army, for a few days for plowing in springtime and a few days for picking in the fall. In the past, unprotected visits to the land ended with many stories of attacks by extremist settlers and burned cars.

This time, soldiers were guarding the villagers from the hilltop where the outpost, Adei Ad, sits. Three soldiers in khaki uniforms were sitting under one of Mr. Abu Aliya’s trees, almost camouflaged among its iridescent leaves while mountain gazelles sprang across the hills.

Adei Ad was established in the late 1990s on state and private Palestinian land, according to Israeli records. Though it was established without any official authorization, the Israeli Ministry of Housing and Construction provided financing for some of the infrastructure.

About 30 families live in trailers at Adei Ad, which has been scheduled for removal for seven years. The settlers have now put up an “eruv,” an elevated string on poles that encircles a community and allows observant Jews to carry objects within the proscribed area on the Sabbath. Mr. Abu Aliya has no idea what the string is for, but he says it runs right through his land.

This year, the harvest was less of a celebration, and more a show of perseverance. The Palestinian Authority governor of the Ramallah district, Laila Ghannam, joined the olive pickers and ate breakfast with the mayor of Turmus Aya under a tree.

“Our presence here is proof that this is our land and we will never give it up,” she said.

Members of a new unit from the authority’s Ministry of Agriculture were also out in the fields with notebooks, documenting the villagers’ complaints and counting the poisoned trees. They took samples of wilting branches to send to an Israeli laboratory for testing in the hope that the results could be used as future evidence in an Israeli court.

Mr. Abu Aliya, who has lost about half of his 300 olive trees, made a promise. “The moment the settlers leave,” he said, “I’ll make a big celebration. I’ll slaughter a buffalo.”