An Israeli concessionaire at the military governor's headquarters in the West Bank city of Nablus was shot in the back and killed today as he walked on a busy street in the center of the city, authorities said.

The murder, witnessed by scores of Arabs, was the latest in a series of attacks on Israelis in the occupied West Bank and in Israel that has sent shock waves through Israeli society and triggered public demands for a crackdown on Palestinian nationalists.

Also today, two Arabs were found blown up near a car in the West Bank village of Tubas, about six miles east of Nablus, in what police said was apparently an accidental detonation of a car bomb.

The daylight gunning down of Albert Buchris in the center of Nablus intensified demands in parliament for imposition of stringent security measures in the West Bank and Gaza Strip, such as the deportation of persons convicted of incitment to terrorism, and for use of the death penalty for convicted terrorists. The Cabinet is scheduled to debate the measures Sunday.

An Army command spokesman said Buchris, a resident of the northern Israeli town of Afula, where two Jewish schoolteachers were kidnaped and murdered last week, allegedly by Arab terrorists, operated a food concession at the military headquarters and was not an Army or government employe.

A mob of angry Israelis gathered outside the Afula police station tonight demanding that the death penalty be imposed on Arab terrorists, the state radio reported. Police reportedly were put on the alert to prevent reprisals against Arabs by extremist settlers in the West Bank.

Prime Minister Shimon Peres, in a tour of the Galilee region, said security measures will be stepped up in the West Bank and in adjoining areas of Israel. He specified deportation of militant Arabs and destruction of homes of terrorist suspects.

An Army spokesman said Buchris was walking alone about 1 p.m. along a busy street when he was shot in the back by an unidentified assailant. Police said Buchris was headed toward a bakery where he bought bagels for his canteen.

The victim managed to stagger to his parked car and drive to the Army headquarters. From there, he was evacuated to a hospital near Tel Aviv by helicopter, authorities said. He died about four hours later.

Nablus and two nearby Palestinian refugee camps were placed under curfew as security forces searched Arab houses.

Palestinian sources said the two Arabs blown up in Tubas had been reported missing Friday after they failed to show up in the village after visiting relatives in Nablus.