WASHINGTON — After months of shuttle diplomacy, the Obama administration is set to plunge into a new round of Mideast peacemaking, bringing Israeli and Palestinian leaders together for face-to-face talks for the first time in nearly two years.

But already low expectations for the talks were jolted even before they began when a Palestinian gunman opened fire on an Israeli vehicle traveling in the West Bank killing four passengers in an attack claimed by the militant Hamas movement. Israeli officials said the shooting was an attempt to sabotage the discussions.

With U.S. officials allowing that success in Thursday’s negotiations may be defined simply as an agreement to meet again, President Obama was getting ready to host Israeli Prime Minister Benjamin Netanyahu and Palestinian President Mahmoud Abbas on Wednesday.

The goal is to formalize a peace agreement in a year’s time that will lead to the creation of a Palestinian state. But with the two sides far apart on all the key issues, the going is expected to be slow and fraught with difficulties.

Tuesday’s deadly shooting near the town of Hebron was a reminder of the fragility of the situation and Israeli Defense Minister Ehud Barak promised a tough response.

Arriving in Washington, Netanyahu condemned the attack.

“Terror will not determine Israel’s borders or the future of the settlements,” he said, referring to a key issue in the negotiations.

Netanyahu’s spokesman, Mark Regev, said the attack would not change this week’s summit, but served to stress the security concerns that Israel plans to make a central issue in the talks. “There is no change. We are committed to peace,” Regev said.

Palestinian Prime Minister Salam Fayyad’s office issued a statement charging that the attack was aimed at undermining his government’s effort to build international support for “the Palestinian position and ending the (Israeli) occupation.”

White House press secretary Robert Gibbs said the U.S. condemns the attack “in the strongest possible terms” and noted that the Palestinian Authority also spoke against it.

“On the eve of the re-launch of direct negotiations between Israelis and Palestinians, this brutal attack underscores how far the enemies of peace will go to try to block progress,” Gibbs said in a statement. “It is crucial that the parties persevere, keep moving forward even through difficult times, and continue working to achieve a just and lasting peace in the region that provides security for all peoples.”

Ahead of Thursday’s sessions, Secretary of State Hillary Rodham Clinton and the administration’s Mideast peace envoy George Mitchell met Tuesday with Abbas and Netanyahu as well as the foreign ministers of Egypt and Jordan and former British Prime Minister Tony Blair, the representative of the “Quartet” of Mideast peacemakers.

State Department spokesman P.J. Crowley said Clinton’s talks were intended to clarify where the parties stand as they head into the talks, which the administrations wants to mark “the reinvigoration of intensive process.”

“We want to see not just a successful relaunch tomorrow, but an understanding that, going forward, the leaders will meet on a regular basis,” he said.

On Wednesday, Abbas and Netanyahu will meet separately with Obama. Then, joined by Jordan’s King Abdullah and Egyptian President Hosni Mubarak, they will attend a White House dinner intended to set the stage for the launch of formal talks a day later at the State Department. Jordan and Egypt are the only two Arab nations with peace deals with Israel.