Israeli security forces today shot and killed a 17-year-old Arab student--the third Palestinian youth to die in a week--as the most violent and protracted riots in six years continued to sweep across the occupied West Bank.

From Jenin, the West Bank's northernmost town, to Hebron in the south, angry crowds of Arab youths pelted Israeli Army patrols with rocks and threw gasoline-filled bottles as the Army rushed in reinforcements in an attempt to quell the disturbances.

General commercial strikes in protest of the shootings and the military government's decision Friday to dissolve El Bireh's municipal council were extended for two more days by the mayors of most major towns in the West Bank, and Arab shopkeepers defied orders by Israeli authorities to reopen.

In the most serious incident today, Mohammed Hamid Badha, 17, was shot dead when Israeli troops opened fire on a crowd of rock-throwing demonstrators at the Deir Ammar refugee camp near Ramallah. Two students were wounded in the gunfire.

An Israeli Army spokesman said that an Army patrol had attempted to disperse the demonstration with tear gas and by firing warning shots into the air and that the soldiers opened fire on the students "only when their lives were in danger."

Army vehicles were also stoned in Ramallah, El Bireh, Hebron and in East Jerusalem, and a molotov cocktail was thrown at a patrol in Jenin.

Officials said the disturbances were the most serious since riots in 1976.

The current violence stems from a test of will between the militantly nationalistic mayors of the West Bank's major Arab cities and Menachem Milson, the new civil administrator of the Israeli military government. Milson has announced plans to develop an alternative leadership to replace Palestinian mayors who openly identify with the Palestine Liberation Organization. As part of that plan, he ordered the dissolution of the El Bireh council.

Today, Israeli police and security forces rounded up El Bireh's municipal employes, who went on strike Friday when the council was disbanded, and drove them to the city hall, where they were ordered to resume work. Palestinian sources in El Bireh said the employes sat at their desks and refused to work.

Palestinian sources in Ramallah charged that a resident of the Jalazoun refugee camp was beaten by soldiers wielding riot sticks. He was identified as Mahmoud Othman, 25, and reported in serious condition at Ramallah Hospital. The Army command spokesman said he had no information on the incident.

Palestinian sources in Nablus said that Israeli soldiers, who had been stoned by students from the roof of the King Talal secondary school, burst into the school, herded about 50 students into classrooms and then exploded tear gas canisters while refusing to allow the students to leave the building. These sources charged that when a doctor arrived, he was prevented from entering the building and that some students who were being driven to the Nablus hospital in private cars were intercepted by security forces and taken to military government headquarters.

The Israeli Army command spokesman had a different version of the incident, saying that as the soldiers attempted to force their way into the barricaded school, they were pelted by rocks from inside and that they fired tear gas only in the courtyard to provide a cover for entering the building. The spokesman denied that students were herded into classrooms and that attempts to take the students to the hospital were blocked.

Israeli Defense Minister Ariel Sharon toured the West Bank, inspecting Ramallah and El Bireh and then meeting in Hebron with Mustafa Dudeen, head of the Village League that has been encouraged by the military government to compete with pro-PLO mayors for political dominance.

In Nablus, Sharon told reporters he was encouraged by the discussions he held with "moderate" Palestinians in the West Bank.

"After 15 years of occupation , for the first time people got up here--Arabs, and not collaborators with Israel--and declared very clearly and without any fear whatsoever that the PLO is not the sole representative of the inhabitants of Judea and Samaria, and they are getting power." Judea and Samaria are the biblical names for the West Bank used by Israeli officials.

"And what's happening now and in recent days shows there is a definite attempt by the PLO and its supporters to contain this development," Sharon added.

In New York, 22 Arab nations today requested "a most urgent meeting" of the U.N. Security Council to halt what they described as an Israeli "reign of terror" against Palestinians in the West Bank, United Press International reported.

The request, filed by Jordan's Ambassador Hazem Nuseibeh on behalf of the 21 other countries, said the "rising crescendo of violence" threatened "peace and security in the region and beyond."

He accused Israel of "deliberate acts of aggression" and asked the council to consider "the grave and rapidly deteriorating situation in the occupied Palestinian and Arab terrritories, including Jerusalem."

Meanwhile, Army Maj. Gen. Ori Or, commander of the central region, said on Israeli Army radio that an investigation has been conducted into Israeli settlers who were seen yesterday firing automatic weapons at Arab demonstrators in Ramallah. Or said the settlers used their Army-issue weapons only when a passing bus filled with Israeli schoolchildren was hit by rocks.

An investigation was continuing also into the fatal shooting Tuesday of an 18-year-old Palestinian student whose body was found Friday near the Shiloh settlement between Ramallah and Nablus. A Jewish settler from Shiloh, whose name has not been released, has been detained for questioning by the Army, which said the settler opened fire on rock-throwing Arab youths but claimed he did not realize he had hit one of them. Palestinian sources who examined the body of the youth, Mohammed Abdullah Suhwain, said the victim appeared to have been beaten before being shot in the head.

The third victim of the current disturbances, Ibrahim Kuran, 17, was fatally shot in the chest by Israeli troops during a demonstration Saturday at the El Bireh city hall.