A new phase in the struggle between supporters of the Palestine Liberation Organization and rival Arabs on the Israeli-occupied West Bank appeared to have begun today with the attempted assassination of a Village League president and the slaying of his son by Arab gunmen in a highway ambush near here.

Yousef Khatib, 60, president of the Ramallah area Village League, was in critical condition in the Hadassah Hospital in Jerusalem after he was shot in the head. His son, Kazim, 23, was killed when gunmen with automatic rifles opened fire on their car as they were driving to the league offices. The gunmen escaped.

In Beirut, the PLO, in a statement released by its news agency, WAFA, claimed responsibility for the attack and said it would "execute all other collaborators with the Zionist enemy throughout our occupied homeland," Associated Press reported.

It was the first reported assassination attempt against the head of a branch of the Village League, the centerpiece of a broad plan by Israeli authorities to build a base of what they consider moderate Palestinians in the West Bank in hopes of weaning them away from the militant politics of the PLO and incorporating them into the autonomous self-governing council envisioned in the Camp David accords.

The Voice of Palestine radio in Beirut had broadcast threats against Khatib's life, and two months ago leaflets began appearing in Ramallah warning officials of the Village League to stop "collaborating" with Israeli authorities.

Khatib, the mukhtar -- or local headman -- of the village of Baleen, eight miles west of here, had been president of the Ramallah region league since last December and often traveled with a protective escort of Israeli troops. He was unaccompanied by Israelis this morning when gunmen opened fire at a crossroads near Ein Arik, about two miles west of here.

The president of the Hebron-based central offices of the West Bank League of Villages, Mustafa Dudeen, condemned the shootings and said he would not be intimidated from forming new league branches.

"Unfortunately, in the Arab world these political crimes are always committed," Dudeen said in a telephone interview.

"These people take revenge in the Arab fashion. Traditionally, they call for blood. We believe these political assassinations will give a very bad atmosphere in the occupied areas," said Dudeen, a Palestinian whom the Israelis allowed to return to the West Bank after serving in the Jordanian government and, before that, in the Egyptian government under President Gamal Abdel Nasser.

Dudeen's headquarters in Hebron is guarded by Israeli troops with a truck-mounted .30-caliber machine gun, and when he travels he is also accompanied by a heavy guard. Some of his supporters openly carry firearms, which for Palestinians is normally unheard of in the West Bank.

The Ramallah area Village League is the smallest of three leagues established by the West Bank military government in the past two years. Dudeen said it encompasses several villages with a combined population of 10,000, compared with the 73 villages he claims to have enlisted in the Hebron area. A Village League has been established in the Bethlehem area and another is being formed in Nablus, Dudeen said.

Palestinians opposed to the program said the leagues have failed to gain popular support, and consist only of a few people who have long been collaborating with Israeli occupation authorities.

Israeli authorities view the Village League plan as the basis of forming associations that could evolve into a nucleus of an accommodating alternative to the PLO and that might go along with whatever formula for West Bank autonomy is negotiated by Egypt, Israel and the United States under the Camp David accords.

The plan was conceived by the new civilian administrator of the West Bank and Gaza Strip, Menachem Milson, when he was Arab affairs adviser to the military governor. Writing recently in Commentary magazine, Milson said that PLO intimidation has stifled moderate voices in the West Bank and that Israel "must create conditions within which moderates in the territories will be able to express their views openly."

With the support of Defense Minister Ariel Sharon, Milson and the occupation military command have conducted a policy of harsh crackdowns on militant nationalists and rewards for those Israel considers moderates.

In the last two days Israel has dynamited the houses of families of persons charged with security offenses and has arrested scores of Palestinians for interrogation. In contrast, those considered moderates have been rewarded with privileges such as travel permits, and some Palestinians who were deported have been repatriated on the basis of promises to curtail radical nationalism.

Authorities blew up another house in the Bethlehem area after a youth who lived there was accused of throwing a firebomb at an Israeli vehicle. Mohammed Warrad, 44, the father of 10 children, collapsed, apparently of a heart attack, shortly after his house was demolished by Israeli troops. He was taken to a hospital.

In a Nablus military court, four Palestinians who were convicted in the May 1980 ambush killing of six Jewish settlers in Hebron and the wounding of 17 others, were sentenced to terms of life imprisonment. Two of the three judges on the panel recommended the death penalty, but imposition of the death sentence requires a unanimous verdict by the court.