Palestinian gunmen killed three Israelis and wounded four others Sunday in drive-by shootings in the West Bank that officials on both sides said would probably hamper efforts to begin peace negotiations.

Only days before Palestinian leader Mahmoud Abbas was scheduled to meet President Bush in Washington, the armed wing of his Fatah movement asserted responsibility for the shootings. The more severe attack occurred at a bus stop popular with Israeli settlers hitchhiking south from Jerusalem. The Israeli death toll -- two young women and a 13-year-old boy, settlement leaders said -- was the highest as the result of a Palestinian attack since July, when a suicide bomber killed five people in the city of Netanya.

The al-Aqsa Martyrs Brigades, Fatah's armed wing, is a diffuse militia whose many regional commands often operate on their own. But Israeli officials sharply criticized Abbas, known commonly as Abu Mazen, for failing to disarm the group and other more radical ones, such as the Islamic Resistance Movement, or Hamas, which does not recognize Israel's right to exist.

"Not only does Abu Mazen not do what he says he'll do in regards to Hamas, but he can't control his own people," said Zalman Shoval, an adviser to Prime Minister Ariel Sharon and a former Israeli ambassador to the United States. "Abu Mazen will have to do some soul-searching about whether he can meet President Bush with clean hands. This seems to be an indication that terrorism will go on, and it will be much harder to begin negotiations as a result."

Palestinian officials also worried that the attack could cast a shadow over Abbas's meeting with Bush, scheduled for Thursday, at a time when the Palestinian leader is hoping to enlist U.S. help in dealing with Sharon.

Facing a restless young guard within his party, Abbas has called on Sharon to withdraw the Israeli military from four West Bank cities and loosen Israel's hold on the borders of the Gaza Strip after ending its 38-year presence in the strip last month. Abbas is hoping to enlist Bush's support for those requests, which could be taken up at a summit between Abbas and Sharon that officials are trying to arrange for this month or early November.

"Whoever did this had in mind undermining the meeting" with Bush, said Saeb Erekat, the chief Palestinian negotiator. "It's undermining our efforts to revive the peace process, and it's also undermining Abu Mazen's political standing."

The late afternoon shootings came soon after an Israeli police patrol near the northern West Bank city of Jenin killed a military commander of Islamic Jihad, a smaller faction that like Hamas is at war with Israel. Israeli military officials said a special police unit came under fire while on patrol and responded by killing the gunman.

But a Palestinian reporter in Jenin interviewed witnesses who said Israeli forces ambushed the car carrying Nahed Ghanem, 27, who emerged to return fire before being killed. Islamic Jihad officials said Ghanem was a senior military commander in the West Bank.

Sharon has demanded that Abbas disarm various Palestinian armed groups, many of them affiliated with political parties, before Israel begins talks within the framework of the U.S.-backed peace plan known as the "road map."

Although Abbas has indicated that he intends to disarm the al-Aqsa Martyrs Brigades as a first step, his weak standing within his own party has made doing so difficult. He was able to formalize a temporary cease-fire involving the armed groups in March that, while reducing violence, has been severely shaken in recent months.

Hamas is campaigning for January parliamentary elections in part on the claim that its armed attacks forced Israel from Gaza. Fatah dissidents, who advocate a more aggressive stance with Israel in the international arena, say Hamas's popularity has risen with a wave of recent arrests by Israel while their own party has little tangible to show voters for advocating a negotiated peace. Some of them suggested that strikes will continue, especially in the West Bank, unless a serious peace process begins.

"We will continue to recognize this as occupation," said Mohammed Hourani, a Fatah member of the Palestinian Legislative Council. "And our right to resist it."

In the bus stop attack at around 4 p.m., military officials said, a blue Subaru slowed as it approached the Gush Etzion junction about 10 miles southwest of Jerusalem. At that hour, the stop is filled with hitchhikers heading home from Jerusalem to a bloc of settlements stretching south to Hebron. Israel has occupied the West Bank since the 1967 Middle East war, and the land is envisioned as part of a future Palestinian state.

Military officials said it was unclear how many were in the car. Witnesses described two bursts of rifle fire coming from it as it slowed near the stop, blockaded with concrete blocks during the most recent Palestinian uprising to protect those waiting from hit-and-run drivers. Three Israelis died at the scene, hospital officials said.

Not long after, a gunman traveling in a car near the settlement of Eli north of Ramallah fired on an Israeli standing by the roadside. Hospital workers said the Israeli, identified as a 14-year-old boy, was seriously injured.

Israeli military officials said Sunday that no military checkpoints had been removed from the West Bank in the past week. But leaders of Israel's main settler movement called on Sharon to close West Bank routes to Palestinian traffic.

Researcher Samuel Sokol contributed to this report.

Israeli paramedics and volunteers collect remains at the scene of the shooting attack at the busy Gush Etzion junction in the West Bank.