JERUSALEM, OCT. 30 -- Three Palestinians were killed and two Israeli Jews were stabbed today as a wave of intercommunal violence surged anew in Israel and the occupied territories despite broad security measures imposed by authorities.

Violence erupted today in Nablus, in the West Bank, where a Palestinian stabbed an Israeli private security guard before being shot dead by a plainclothes officer. In Bnei Brak, a suburb of Tel Aviv, one Arab was killed and two injured when a bomb they were trying to assemble exploded in a vegetable store, authorities said.

Later, soldiers shot and killed a Palestinian in Tulkarm, in the West Bank, after encountering "a group of suspected terrorists," Israeli radio said. In East Jerusalem, an Israeli policeman was lightly injured when a Palestinian stabbed him in the neck, police said. The attacker was arrested.

The incidents, the first in a week, punctured an uneasy calm that followed the reopening of the border between the occupied territories and Israel on Sunday. The army had sealed off the territories for four days last week, forcibly separating Israelis from Palestinians and effectively recreating Israel's pre-1967 borders, in an effort to halt a spiral of violence in which three Israelis and three Palestinians died.

Palestinian militants have sought revenge for the Temple Mount killings of 20 Arabs earlier this month, using knives and bombs that until now were forsworn by the leadership of the 34-month-old intifada, or uprising against Israeli rule.

In Nablus today, masked Palestinians announced by loudspeaker that the latest assailant, identified as Haitham Jamla, 18, was a member of the Islamic Jihad, a militant Moslem group outlawed by Israel on Monday.

According to Israeli accounts, Jamla attacked a private Israeli security guard who was escorting a gasoline tanker into Nablus. The guard was stabbed three times in the back, army radio said, before a passing plainclothes Israeli security agent shot the Palestinian to death. Officials said the security guard suffered moderate wounds.

In Bnei Brak, populated mostly by Orthodox Jews, the attempted bombing reportedly was carried out by three Palestinians from the territories who work in a store and sleep there overnight. Since last week, authorities have tried to enforce a law banning Arabs from the West Bank and Gaza Strip from staying in Israel overnight, but many continue to do so.

Tens of thousands of Palestinians from the occupied territories who commute to jobs in Israel have been gradually returning to work this week, despite mounting fear and antagonism among both the workers and their Israeli employers. Israeli news media have published reports suggesting that thousands of Arabs have been fired in recent days, although economists say Israel remains as dependent on the more than 100,000 Palestinians it employs as the Palestinian economy is on their salaries.

For several days, Defense Minister Moshe Arens and military commanders have been preparing new security measures intended to preserve the linkage between Israel and the territories while reducing the danger of attacks by Palestinian militants. The issue is a sensitive one for the government of Prime Minister Yitzhak Shamir, which wants to avoid reestablishing a border between Israel and the territories, but is under pressure from Israelis who were angered and frightened by the recent violence.

According to reports in the Israeli press today, the army's solution will be to increase the number of Palestinians banned from entering Israel from the present 8,000 to 20,000. The government also will crack down on the employers of the estimated 50,000 Palestinians who now work in Israel without legal permits. About 60,000 Arabs from the territories already have working papers.

In a speech to American Jewish fund-raisers Monday night, Shamir promised to crack down on Palestinian militants, saying, "We shall react to them whether they use stones or firebombs, knives or other weapons." He added: "We shall not expose our citizens to danger. We shall build a wall of steel and love around our people, as we face threats."