Sen. Barack Obama stepped gingerly through the intractable politics of the Middle East yesterday, offering resolute support for Israel's security, warning that Iran's acquisition of nuclear weapons would be a "game-changing" event for the world, and pledging to make peace talks between Israelis and Palestinians one of his highest priorities if he becomes president.

By motorcade and helicopter, in private meetings and public appearances, the Democratic presidential candidate moved from the Yad Vashem holocaust museum in Jerusalem to the Palestinian Authority headquarters in the West Bank city of Ramallah to the southern Israeli town of Sderot just outside the Hamas-controlled Gaza Strip.

Obama used Sderot's police station and a backdrop of racks of spent rockets from Gaza to declare his "unshakable commitment to Israel's security." He added: "The state of Israel faces determined enemies who seek its destruction. But it also has a friend and ally in the United States that will always stand by the people of Israel."

Today the presumptive Democratic nominee will turn his attention to Europe. He will hold the biggest public event of his overseas tour at Berlin's Tiergarten Park in the evening.

With an eye to Jewish voters back in the United States and to public opinion here, Obama defended himself yesterday as a staunch and longtime friend of Israel and said he has a voting record that proves it. "The way you know where somebody's going is where have they been," he said. "And I've been with Israel for many, many years now."

The Illinois Democrat has faced skepticism among some Jewish voters in the United States over whether he would be a reliable supporter of Israel and is viewed quizzically as well by many Israelis, who don't know quite what to make of his unusual name and his slim track record in foreign policy.

Obama's statements of support for the Jewish state have gone over well in Israel, but there is widespread apprehension that he will be more sympathetic to Palestinian interests than previous American presidents. His rival, presumptive Republican nominee John McCain, is better known here and seen as a more dependable protector of the country's interests. McCain visited Israel last spring, also stopping in Sderot.

Obama again clarified a statement he made to the American Israel Public Affairs Committee in June, when he declared that he supported making Jerusalem the "undivided" capital of Israel. That comment drew sharp protest from Palestinians, and Obama quickly corrected the statement at the time, saying by "undivided" he meant a city not carved up by barbed wire as it was at one time.

"That's an issue that has to be dealt with with the parties involved, the Palestinians and the Israelis," he said in Sderot. "And it's not the job of the United States to dictate the form in which that will take."

Obama's day was a succession of meetings with top Israeli and Palestinian officials, interspersed with his few public events. He met over dinner with Israeli Prime Minister Ehud Olmert, but before that he had already seen President Shimon Peres, Defense Minister and Labor Party leader Ehud Barak, Likud Party leader Benjamin Netanyahu, and Foreign Minister Tzipi Livni.

He also took time for the short drive north to Ramallah for face-to-face meetings with Palestinian Authority President Mahmoud Abbas.

In Sderot, Obama appeared anxious to deliver a stern message about Iran, a topic that was raised in his meetings with Israeli leaders. "A nuclear Iran would be a game-changing situation not just in the Middle East, but around the world," he said. "That could shred the nuclear-proliferation framework and possibly allow terrorists to get their hand on such weapons."

Obama said he would try to "mobilize the international community, to offer a series of big sticks and big carrots to the Iranian regime to stand down on nuclear weapons. We have to do it now."

Although Obama received a red-carpet welcome from Israeli and Palestinian politicians, much of the public on both sides was only dimly aware of his presence here.