JERUSALEM -- At the roadblock in the neighborhood called French Hill, the young men of Israel's Civil Guard were on patrol and briskly waving through every car, until a small white Fiat appeared and the atmosphere suddenly changed.
Chaim, the policeman in charge, would explain later that the Fiat was different because he suspected the driver wasn't going to stop in the evening gloom. But the driver stopped exactly where Chaim pointed with his flashlight.
Everyone had seen the number and color of the license plate, the giveaways that the car belonged to a Palestinian from East Jerusalem. The civilians on patrol were alarmed that a Palestinian was about to enter a Jewish neighborhood at night.
In this city, where coexistence between Arabs and Jews was supposed to become the norm, any unexpected contact between the two groups is now like bringing a flame close to a volatile fuel.
For many people, Jerusalem has come to seem a dangerous place within the past month. Police shot to death at least 18 Arabs in a clash on the Temple Mount, an Arab stabbed three Israelis to death, and Israelis attacked Arabs on the street. Each side has sought to justify its violent acts with claims that they are rightful revenge for violence of the past.
"We have much more extreme cases than before," said Yaacov Shuval, an assistant police commissioner. "There's gotten to be a certain level of risk, and a situation that demands activity from police. This calls for everyone to be on a higher state of alert."
Israelis have responded by volunteering for the Civil Guard, an auxiliary police force designed to reassure the public with highly visible patrols.
One rough gauge of public confidence is the change in the number of volunteers. When the number goes up, confidence is heading down, and the numbers are now approaching an all-time high.
Since Iraq invaded Kuwait Aug. 2 and increased fears of a regional war, the number of volunteers in Jerusalem has increased almost 30 percent, to 3,600. The number of civilians on patrol on an average night has jumped to 250 from 110, and police want to expand the night patrols into patrols 24 hours a day.
"There's a rush to gun shops, and people are buying knives and putting them under their pillows," said Israel Eran, police superintendent. "But the only organization that has authority and can give training and supervision is the Civil Guard."
It was established in 1974, after Palestinian guerrillas infiltrating from Lebanon carried out a series of attacks in which dozens of Israeli civilians, many of them children, were killed. Ever since, civilian volunteers trained by the police have been on guard at schools and playgrounds and patrolling their neighborhoods.
"The Civil Guard is needed because the police can't handle everything they're supposed to do," Mr. Shuval said. "The people in Israel hate armies and hate wars. But when there's no choice, people are mobilized and rally to the flag."
French Hill is one of the Jewish neighborhoods established to surround the Arab areas of East Jerusalem, territory Israel captured and annexed in 1967 and declared to be a permanent part of an indivisible city.
A series of bypass roads attach French Hill to other Jewish neighborhoods in such a way that Israelis can cross the city without entering areas where Arabs live. And not by accident, the four- and five-story apartment buildings were built on the high ground dominating the eastern approaches to the city, making French Hill a residential fortress.
On one side is the Shuafat refugee camp, on another the Palestinian neighborhood called Issawiya, places the Civil Guard does not dare to go even in a police van with a flashing blue light.
"Any Israeli car that goes in there unprotected -- without screens for the windows, all sorts of things -- something happens," Chaim said.
He was leading a five-member patrol. It included Gaddi, 17, especially gung-ho and two weeks away from beginning his three years of army service; Lior, also 17, entering the army next year; Menashe, 23, a student at a religious school; and Yossi, 25, three months out of the air force and about to start a civilian job.
Only first names were given, following security regulations for police and the military.
The patrol's three-hour shift combined dull routine with a chance to exercise considerable authority over anyone they saw.
"You know, in Jerusalem this is not a very good time," said Gaddi, carrying an M-1 carbine. "I want my people to be able to have a good night's sleep. Anyone who looks OK, he can go through."
Few if any Arabs can pass that test. An Arab spotted after dark on the streets of French Hill was stopped, asked for his papers and asked why he was there.
"All very polite," Chaim said. "We treat people in the nicest way possible."
A large part of each night's work is driving in the van to parking lots, where more than a dozen Israeli cars have been set on fire in the past year and where an intruder could hide. All was quiet this night.
It was no different at the roadblock, even when the Fiat arrived, the Palestinian at the wheel obeying the order that he park behind the van.
Similar scenes are enacted hundreds of time each day -- a soldier, a policeman, a civilian waving a Palestinian to a stop and beginning a search.
Hands shaking, the gray-haired driver of the Fiat handed over his identity papers. And then those of his passengers. And then the registration papers for the car. And then opened the trunk. Why, Menashe asked, was he here? Why come to French Hill to get to an Arab neighborhood when there are other routes?
There was nothing for the driver to do but to take back his papers, turn his car around and leave French Hill.