Occupied West Bank - Their cars cruise slowly through the teeming streets of Arab villages and towns stretching all the way from Jenin, in the north, to ancient Hebron, the West Bank's southermost city.

Poking out of the windows are the menacing black barrels of M16 automatic rifles and the snub noses of Israeli-made Uzi submachine guns.

Or they walk in pairs down the center of the streets, dressed in civilian clothes and wearing the traditional yarmulkes, casually fingering the webbed slings, of their rifles and ignoring the resentful stares of Arabs sitting in the shadows of cafes, drinking strong turkish coffee and playing dominoes.

If a group of Palestinian students begins assembling with the telltale gear of an imminent demostration - sacks of stones and bags of wet sand with which to douse tear-gas canisters - the ever-present sentinels appear almost magically, waving their weapons and occasionally opening fire to disperse the crowd.

They are the unofficial, self-appointed gurdians of the Jewish presence in the West Bank - a loose network of ad hoc vigilante squads who claim they are the vanguard of a new civillian security force that will maintain law and order in the occupied territory if the Israeli Army reduces its force as a result of proposed Palestinian autonomy.

Nobody knows their numbers and, as yet, they have no name and no acknowledge central leadership. Yet the vigilantes already are of serious concern to the government of Prime Minsiter Menachem Begin and to the military government of the occupied territoties.

Two Arab youths have been killed and several seriously injured as a result of clashes between the armed Jewish civilian settlers and Arabs in the last two months. Officials fear that the problem will worsen if the West Bank autonomy Negotiations lead to a reduced military presence in Palestinian cities and towns.

The civilian "security patrols," ad hoc punishment handed out to rock-throwing Arab youths and, more recently, the terrorizing of Arab families in their homes has been steadily heightening tendions between Arabs and Jewish settlers. it comes at a time when Israeli leaders are attempting to convince Egypt that Palestinians and Jews can live in peaceful coexistence.

Critics of the vigilantes say their aim is to scuttle the autonomy negotiations, in the belief that those talkes will lead inevitably to a Palestinian state. Exploiting divided Israeli public opinion and capitalizing on increased Arab protests, the vigilantes are not as interest in self-protection as they are bent upon perpetuating Israeli occupation of the West Bank, moderate officials say.

Vigilantism and curbside justice are nothing new to the West Bank. In 1976, civilian settlers disrupted a demonstration in Hepburn and took three Arab "prisoners" to a makeshift cell the the basement of the nearby Kiryat Arba settlement, after which the Arabs said they were stripped and made to face a snarling German shepherd.

Nevertheless, after a two-year decline in such incidents, coinciding with the growing politicization of West Bank youths, clashes between settlers and Arabs seem to be on the rise again.

Abdul Aziz, a 42-year-old part-time messenger in city hall, was watching television Saturday nigh with his wife and four children in their tiny stone house in Hebron's casbah when they heard a frighful pounding on their door. Four armed men burst in side, shouting in Hebrew and waving their weapons.

"Why are you living here?" one demanded, shifting to Arabic, while the others, dressed in civilian clothes and wearing skullcaps, began wrecking the living room.

On cracked the front of the television set with his boot, while others smashed a glass coffee table, broke a chair and threw glasses of hot tea on the floor.

"You are living in a Jewish house. Get out!" one tall Hebrew-speaking man shouted at Aziz, who tried to explain that his father and grandfather had lived in the house. The men began beating Aziz as his children cried hysterically and his wife ran screaming outside.

Aziz, whose ear still showed some wounds, said one of his young daughters and shouting, "God kill Sadat," because she associated the beating of her father with the peace treaty signed by Begin and Egyptian President Anwar Sadat.

Asked what the Hebron Arabs would do if the intruders - who apparently had attended a rally that night in support of ultranationalist women occupying a derelict building they say is Jewish-owned - were to return, Aziz answered:

"If they come to kill the Arabs of Hebron, the people will fight back. Everybody is buying knives.The people will not stand still."

Although the authorities suspect the intruders are from Rabbi Meir Kahane's militant Jewish Defense League, headquartered in the nearby Kiryat Arba settlement, no arrests have been made. Aziz, who gave police a composite sketch of the men, said he had often seen them in the Arab open-air market "pushing people around."

Before the night was over, three houses in the casbah had been similarly terrorized, city officials said. Several more on the outskirts of town were reportedly stoned by the roaming gang.

At a nearby clinic owned by Dr. Hammad Fawzi Karaki, a nurse, Hadra Ahmed hassani, said she was tending to patients in midmorning when a gang of armed men, most wearing yarmulkes, burst in. They began tearing pictures off the wall and shouting in English, "This is our house. Leave," she said.

A week earlier,m a pharmacy next door was broken into by men who claimed the building was Jewish owned before the massacre of 1929, when Arabs killed 60 pious Jews. Since then, no Jew has lived in the city.

On the outskirts of town, vandals with a power saw recently destroyed 500 grape vines tended by an Arab farmer. About 35 miles north, near Ramallah, armed civilians, enraged by the stoning of a schoolbus, opened fire over the heads of demonstrating Arabs. They then burst into an Arab secondary school and abducted its principal, taking him to a settlement for "questioning" before releasing him to Israeli military authorities.

Still farther north, in the hamlet of Bir Zeit, armed civilians from the Neve Tzuf settlement confiscated the identity cards of merchants and forced them to close their shops because Israeli settlers were pelted by rocks. Almost daily, armed patrols still drive through the hamlet.

In March, two high school students were shot to death in the Arab village of Halhul when civilian settlers opened fire on rockthrowing protesters. Last month, during a demonstration at Bir Zeit University, a student was shot when Jewish settlers opened fire "in the air" to disperse them.

On settler, who admitted shooting to disperse the crowd, later said he had been issued new ammunition by the army because he had emptied his weapon's magazine. No one has been arrested in the incident, except 14 Arab students who were jailed for three months for demonstrating.

Eliakim Haetzni, a leader of the Council of Jewish Settlements, has issued an appeal in the Ultranationalist Land of Israel Movement's magazine for vigilante recruits. He wrote, "What will happen if the government of Israel . . . withdraws [from the West Bank], taking with it Israeli law, judges and policemen, leaving us alone to face an emerging Palestinian government?"

"The betrayed and the abandoned," Haetzni said, would have to provide their own law judges and policemen.

Haetzni says the civilian force will guard the settlements, patrol the surrounding political meeting and demonstrations.

"If they set up barriers there, we'll dismantle them by force. If they raise the [Palestine Liberation Organization] flag, we'll pull it down . . . We'll move in on our own," says Haetzni.

Even moderate voices in Kiryat Arba, while criticizing such tactics as Saturday night's raids on Arab homes, say that rising tensions in the West Bank call for a certain amount of force.

Rachael Klein, a leader of the Kiryat Arba women's committee, said of Saturday night's raids, "I'm not going to deny something I don't know. I haven't had time to check. Maybe Arabs did it themselves, but it certainly is not constructive."

Asked what would happen if the Army withdrew from Hebron, Klein said, "I don't think it will happen, but if it comes to a confrontation then, well, it comes to a confrontation."

Fahd Kawasma, mayor of Hebron, said in an interview he cannot understand why the vigilantes involved in the Saturday night raids have not been arrested.

"If a bomb goes off somewhere, they [the Israeli security forces] round up 30, 50 or 100 people before it gets dark.Why can't they collect 10 persons, or one, from Kiryat Arba in a week? Do you believe the military governor doesn't know the names?" asked Kawasma.

The vigilantes "want to put their fist on Arab Hebron, ti make us afraid, to punish us before we rise up," Kawasma said. He said he was afraid only that more provocations by roaming bands of settlers would result in a clash that would bring the Israeli Army into the city in force.

So far, the military government has announced no arrests in the Saturday night incidents and it has maintained a strict silence on the matter. The Cabinet and Begin, however, have strongly condemned the raids and have ordered a police investigation. Lt. Gen. Benjamin Ben-Eliezer, West Bank commander, would not meet with a reporter to discuss the issue, the occupied territories was also unavailable.

An aide to Prime Minister Begin, however, called the settlers' claim of inadequate army protection "ridiculous," adding, "that's what vigilante groups say everywhere - here or in the United States, or anywhere - that the police aren't doing their job, so they have to do it. The army is providing plenty of protection, and now they have the added job of seeing that the vigilantes don't take the law into their own hands. It's a problem."* CAPTION: Picture 1, Settlers from Kiryat Arba, where the Jewish Defense League is headquartered, walk through the streets of Hebron. One of the men carries an M16 rifle. by Gideon Gitai; Map, no caption, By Dave Cook-The Washington Post; Picture 2, The mayor of Hebron, Fahd Kawasma, questions sincerity of Israeli military.; Pictures 3, Hadra Ahmed Hassani, a nurse, tells of viligantes breaking into her clinic and claiming if for Israeli settlers.