ETZION MILITARY BASE, West Bank — More than 300 Palestinians showed up at an Israeli military base in the West Bank recently, hoping they could win the lifting of security bans that prevent them for entering Israel.

But they were also anxious. Talking in small groups, they recounted past experiences where some had been asked to spy on their neighbors in exchange for a permit — a gut-wrenching choice. Permits mean higher-paying jobs in Israel, but suspected informers are shunned or attacked in their communities.

The men waiting outside the Etzion base had seized the offer of security ban reviews as a rare chance to access a secretive system. But they also feared the "clearance campaign" makes it more convenient for Israel's Shin Bet security service to gather information about them.

"They control the lives of the people, deciding who can come and who can go," said Majed Ghayada, 35, one of those at the gate who learned of his security block last fall when his permit request was rejected, without explanation.

Security bans are the hidden centerpiece of a permit system that Palestinians consider the ultimate tool of control in Israel's half-century-old military occupation.

The impact of the permits system reverberates in numerous ways, directly or indirectly affecting the lives of nearly all the 4.5 million Palestinians living in the West Bank and Gaza Strip. Having a permit can determine where Palestinians work or study, whether they can visit relatives or afford to get married, even whom they marry.

The system, mainly run by a military administration known by its acronym COGAT, has swelled over into a sprawling bureaucracy with intricate categories and arcane rules, often opaque and confusing, according to multiple interviews with those involved in and affected by the system. The result often confounds Palestinians' attempts to live a semblance of a normal life.

Israel portrays permits as good-will gestures meant to improve the lives of Palestinians. It says the system is crucial to shield against what it says are ongoing attempts by Palestinian militants to carry out attacks.

Hundreds of Israelis were killed in bombings and shootings over a decade ago, and Palestinian militants keep trying to carry out attacks in Israel, said retired Col. Grisha Yakubovich, a veteran of the Civil Administration, which is part of the COGAT system. "So you need to check everybody," he said.

Rights activists say the system is unique because of its sophistication and the large number of people it controls— 2.5 million in the West Bank and 2 million in Gaza.

Israel typically issues several hundred thousand entry permits a year for West Bankers, ranging from day passes to those valid for several months, for work, health care, study and other purposes.

In Gaza, under blockade since a 2007 takeover by the militant Hamas, even the small number of permits for "exceptional" entry to Israel plummeted. Last year, fewer than 6,000 people a month left on average, roughly half the level of 2016, according to the Israeli rights group Gisha.

COGAT did not respond to repeated requests for comment on the permit system. But it has defended the shrinking permit numbers from Gaza, saying Hamas exploits travelers to smuggle money or weapons.

Underpinning the permit system is the absence of a recognized border between Israel and the war-won territories. Israel never annexed the West Bank, even as it built settlements there. Israelis move freely in and out of the West Bank. But Israel argues that Palestinians don't have an inherent right of entry to pre-1967 Israel and east Jerusalem, their traditional political, cultural and commercial hub, or to travel between the West Bank and Gaza.

Yael Berda, a former Israeli lawyer, said she believes a key objective of the permit system is to enable the Shin Bet to recruit informers providing low-grade information.

Shin Bet agents use seemingly irrelevant snippets of information to create the impression of omnipotence, she said. She recalled how agents asked one of her clients about a needlepoint rendering of a Muslim shrine on display in his living room.

"At that moment, the person thinks their whole life is an open book, that he shouldn't hide anything," said Berda, who has written a book about the permit system.

In a statement to The Associated Press, the Shin Bet denied a hidden agenda, saying that security blocks are "solely derived from security considerations and the prevention of terrorism."

Tens of thousands of West Bankers are believed to have security bans on them. The Shin Bet refuses to specify how many. The cause of security blocks is often a mystery. Anyone who ever served prison time is almost certain to have one, but others who are banned were never in an Israeli prison.

At the Etzion base, Palestinians handed their Israeli-issued ID cards to soldiers last week.

Several younger men were called for interviews. One emerged dejected. The 26-year-old said the agent told him that before removing the ban — in place since a one-year prison term for a security offense in 2013 — they first had to "build a bridge of trust." The man, who spoke on condition of anonymity for fear of repercussions, rejected what he saw as an attempt to recruit him.

Only a small number of people saw their bans lifted that day, according to those present.

Quarry owner Mohammed Thawabta said he had been blocked at the beginning of the year after seven years of having his trader permit renewed without problems. The 39-year-old sells $1.7 million of cut stones a year, including to Israel.

By early afternoon, a soldier handed back Thawabta's ID, telling him the ban remains in place.

"I was so disappointed because I went there full of hope ... because I'm a businessman and I was never engaged in any problem with anyone," Thawabta later said by phone.

He needs the permit to deal with his Israeli customers, he said, adding that "nothing is in my hand."

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Associated Press writer Fares Akram in Gaza City, Gaza Strip, contributed to this report.