Some 200 Palestinian men crowded behind the hip-high, red barrier at the Israeli checkpoint. When one asked when they would be let through, a young soldier shouted, ``Shut up!''

Every day, tensions run high at roadblocks that have severely restricted Palestinian movement in the West Bank in more than three years of violence.

The Hawara checkpoint is one of only three passages into Nablus, the West Bank's biggest city, and many of the men had been waiting for two hours to get in when the soldier demanded they form two neat lines. When no one budged, he grabbed several and roughly shoved them into line.

Amir Fattouh, 23, a third-year student of international law, stood quietly. Soldiers had already seized his ID card for complaining once, he said. ``If I say anything, they'll keep my ID for a long time.''

Israel calls the blockade an effective tool in its war on terror and says restrictions are eased when possible.

Critics say the lockdown has devastated the Palestinian economy -- three in five Palestinians now live on less than $2 a day -- and argue it has only increased support for militants while failing to deter attacks. Dozens of Palestinian attackers have slipped through since 2000, killing nearly 900 people in bombings and shootings.

Some human rights activists believe Israel is using the blockade intentionally to punish civilians, hoping they would then pressure their leaders to rein in militants.

The top U.N. official in the region, Terje Roed-Larsen, keeps urging Israel to ease the closure, but he concedes that ``Israel is in a real dilemma, because a total opening might lead to new terrorist attacks in Israel.''

The restrictions began immediately after the outbreak of fighting in September 2000. Israel's government closed its territory to residents of the West Bank and Gaza Strip, including more than 130,000 laborers whose earnings from jobs in Israel were the backbone of the Palestinian economy.

In the West Bank, troops also have imposed lengthy ``internal closures,'' confining residents to their communities. In Gaza, the Israelis sometime restrict travel along the main north-south road, the lifeline of the crowded coastal strip.

A U.N. survey in November found 757 barriers in the West Bank, including 73 manned roadblocks, 464 earth mounds, 58 ditches and 95 concrete blocks preventing the movement of cars. The army says it runs 45-47 manned roadblocks, in addition to roving checkpoints. Israel also is building a security barrier through much of the West Bank, further hampering Palestinian movement.

In other conflict zones, such as Aceh in Indonesia and Chechnya in Russia, military roadblocks carve up regions to monitor traffic, but travel is permitted in principle, with bribes further greasing the flow.

Israel's restrictions are more sweeping. West Bank residents have to apply for military permits to move between towns, and Nablus and the town of Jenin, considered hotbeds of militancy, are under even tighter closure.

In Nablus, men ages 16-35 cannot leave or enter the city, except for high school and university students, teachers and medical staff. Women and older men are generally allowed passage through the three roadblocks ringing the city.

The severity of movement restrictions ebbs and flows, and Israel has eased travel bans somewhat in recent weeks. Several checkpoints have been removed, and 21,000 laborers and 10,000 merchants are being allowed to enter Israel. In January, Israel plans to install special biometric sensors at the Erez crossing in Gaza to speed up the passage of thousands of workers.

Decisions at the roadblocks often seem arbitrary.

At the Hawara checkpoint, a Palestinian man pulled out an X-ray to show he had a doctor's appointment in Nablus, but soldiers denied him entry, while another coughed convincingly enough to get through. Some were picked out of line, had their ID cards taken and were ordered to stand to the side for a more thorough check.

In the afternoon, with the passage closed due to a security alert, the crowd swelled to about 300. The half-dozen soldiers became increasingly harried, trying to push people back. One soldier used a rifle held by stock and barrel as a battering ram.

A man holding a sleeping toddler on his shoulder was inadvertently pushed forward by the crowd. A soldier, gesturing with his gun, ordered him back, and when the man was unable to move, sent him to the back of the line, condemning him to spend more hours waiting.

An Israeli major seized an Associated Press photographer's camera, preventing him from taking pictures at Hawara -- an apparent violation of army regulations. At the Qalandiya checkpoint, a soldier seized an AP reporter's tape recorder. The camera and the tape recorder were eventually returned.

Many Palestinians avoid the roadblocks and try to sneak past soldiers along bumpy back roads. Taxi drivers caught by army patrols have their car keys taken and passengers are detained for hours, sometimes all day.

In Nablus, 55 taxi drivers have switched from customary Mercedes seven- seaters to all-terrain vehicles -- most stolen from Israel -- to take passengers across the mountains. They hire lookouts who alert them by cell phone to soldiers lying in wait.

Moayad Salwaha, 41, who lives in the village of Assira al-Shamaliya near Nablus and teaches math in a city high school, prefers the mountain road even though he could pass through a checkpoint.

``We sometimes stand at the roadblock with our students, and the soldiers talk to us without respect. This is very unpleasant,'' he said. Last month, he got caught by the army five times.

A senior army commander in the Nablus district said the clampdown is needed to stop suicide bombers from sneaking out of the city. He said that over the past 18 months, his men had caught 120 would-be bombers in various stages of preparations, including 20 with explosives strapped to their bodies.

Of the 105 Palestinians who succeeded in carrying out bombings over the past three years, about 40 came from the Nablus area.

The officer, who spoke on condition of anonymity, said he is trying to inflict as little hardship as possible, but ``security comes before everything.'' He said he allows his soldiers to seize car keys for 24 hours and detain anyone violating the closure for up to four hours.

Two soldiers under his command were recently sentenced to 28 days each in military jail, the officer said, one for beating a Palestinian and the other for smashing a car's headlights.

One reserve corporal who has done roadblock duty said soldiers are often tired from long shifts and are anxious because there have been more than a dozen deadly attacks on checkpoints. Orders also change at a crazy pace, leaving soldiers confused, said the soldier, who spoke on condition of anonymity. Even soldiers arriving with good will toward Palestinians often lose it quickly because of constant arguments, he said.

Noam Hofstatter of the Israeli rights group B'tselem said that ``every soldier can decide what he wants to do with specific Palestinians, according to his mood.''