JERUSALEM — Presidential hopeful Barack Obama donned a Jewish skullcap at Israel's Holocaust memorial today and vowed to preserve America's close ties with Israel in a dramatic visit to the Holy Land in which he also promised the Palestinians to push vigorously to win them a state.

Obama clearly was trying to allay fears on both sides on how he would tackle their stubborn conflict.

Many Israelis are concerned that Obama — a first-term U.S. senator with little foreign policy experience — would push Israel too hard in negotiations with the Palestinians. His family's Muslim roots have added to the unease, even though Obama is a Christian.

Palestinians doubt Obama or any other U.S. leader would reverse what they see as Washington's bias toward Israel.

"I'm here on this trip to reaffirm the special relationship between Israel and the United States and my abiding commitment to Israel's security and my hope that I can serve as an effective partner, whether as a U.S. senator or as president," Obama during a visit to the official residence of Israeli President Shimon Peres.

A 30-minute drive away, in the West Bank town of Ramallah, Obama assured Palestinian leaders he'd get involved in the Mideast conflict quickly, a top Palestinian official said.

In his meeting with Palestinian President Mahmoud Abbas, Obama confirmed "that he will be a constructive partner in the peace process" and would not "waste a minute" if elected, Abbas aide Saeb Erekat said.

Obama is visiting at a time of great political turmoil in the region that has jeopardized prospects for Mideast peace. Israeli Prime Minister Ehud Olmert is under investigation in a corruption probe that threatens to topple him. And the Palestinians are deeply divided, with Abbas' forces in charge of the West Bank and the Gaza Strip ruled by Islamic Hamas militants.

Obama plunged into the intricacies of the region's longest-running conflict with a packed schedule of meetings with Israeli and Palestinian leaders.

At Israel's Yad Vashem Holocaust memorial, he laid a wreath of white chrysanthemums and lisianthus and lit a memorial flame. "Despite this record of monumental tragedy, this ultimately is a place of hope," he said.

"At a time of great peril and torment, war and strife, we are blessed to have such a powerful reminder of man's potential for great evil, but also our capacity to rise up from tragedy and remake our world," he wrote in the visitors' book.

American tourists who passed by him at the memorial told him, "Remember what you see here," and he replied, "Yes, I understand, I understand," said Yad Vashem's director, Avner Shalev.

Security guards at the memorial kept back the few American and European visitors who had hoped to get a closer glimpse of the presidential contender.

But the somberness of the occasion at Yad Vashem also gave way to moments of warmth and lightheartedness.

Peres gave him an effusive welcome, saying he had read Obama's two books and was "moved" by them. The Israeli president handed Obama an English translation of a book he wrote, "The Imaginary Voyage: With Theodor Herzl in Israel." Obama asked him to sign and dedicate the book, Peres' office said in a statement.

Obama praised Israel's accomplishments 60 years after its creation, and he complimented the 84-year-old Israeli president on his youthful appearance.

"I also want to get his recipe for looking as good he does," Obama quipped.

An aide to the president said Obama showed a "strong grasp" of regional affairs and that "he said he came to listen and learn." The aide spoke on condition of anonymity because the meeting was not open to the public.

Earlier in the day, Obama met with Israeli Defense Minister Ehud Barak and parliamentary opposition leader Benjamin Netanyahu, whose Likud Party takes a hard line against the Palestinians. He was to meet with Olmert in the evening, after visiting a southern Israeli town that's been bombarded by Palestinian rocket fire from the Gaza Strip.

Israeli officials said their talks with Obama included discussions about Iran's nuclear ambitions. Many Israelis are worried by Obama's willingness to talk to Tehran, the Jewish state's bitterest enemy.

Obama met with Barak and Netanyahu at Jerusalem's posh King David Hotel, where an "Israel for Obama" campaign poster was draped over an armchair in the lobby. The poster included Obama's campaign slogan — "Change you can believe in" — in Hebrew.

Some Israelis who support Obama hope he will take a stronger hand with Israel when it ignores its commitments to the U.S. to halt settlement building and dismantle settlement satellites known as outposts.

"In general, I think tough love is better than a free hand," said the head of the "Israel for Obama" campaign, Samson Altman-Schevitz. He moved to Israel two years ago from Chicago, where Obama's wife, Michelle, was his adviser at the University of Chicago.

Obama left Abbas' headquarters without speaking to reporters. But on Tuesday, he cautioned it is "unrealistic to expect that a U.S. president alone can suddenly snap his fingers and bring about peace in this region."

His meeting with the Palestinians stands in contrast to the decision by Republican presidential hopeful John McCain to visit only Israel in March, without stopping in the West Bank.

On the road leading to Abbas' headquarters on Wednesday, police were out in full force, standing 10 yards apart and outfitted in full battle regalia, wearing camouflage uniforms, helmets and bulletproof vests and carrying truncheons and assault rifles.

The Illinois Democrat is working to shore up support among U.S. Jewish voters. Many supported Hillary Rodham Clinton in the battle for the party's presidential nomination, and some have questioned his commitment to Israel.

Obama arrived in Israel Tuesday night from neighboring Jordan and is due to leave for Germany early on Thursday.

Hours before his arrival, a Palestinian man wreaked havoc in downtown Jerusalem — several hundred yards from Obama's hotel — by plowing a front-end loader into cars and a bus. Five people were wounded before a bystander and a policeman shot him dead in the second such incident in the city in less than a month.

A spokeswoman for Yad Vashem, Estee Yaari, said at the end of his visit there, Obama met with the policeman and told him, "Oh, I thought they would have given you the day off."