His speech Thursday from Cairo University will try to soften the fury toward the United States among so many of the world's 1.5 billion Muslims, ignited by the U.S. occupation of Iraq and the hands-off attitude toward the Israeli-Palestinian conflict of his predecessor George W. Bush.
Mr. Obama's offer of a new beginning is seen as an attempt to stem the growing influence of extremists - particularly Iran, with its regional and nuclear ambitions - and to bolster moderate Muslim allies.
It comes just days ahead of crucial elections in Lebanon and Iran - where the appeal of militancy will be put to the test - and amid worsening violence in Iraq, Afghanistan and Pakistan.
The American leader's soaring oratory and Muslim roots have kindled hope among Muslims. But they will judge him by his actions, not his words, said 20-year-old Mohammed Wasel, sipping sugar cane juice with friends after mosque prayers in Cairo's Abbasiya neighborhood.
"There will be a lot of talk, but I seriously want to see something real coming out of this speech, something tangible," Wasel said, expressing a view shared by an Eritrean social worker in Rome, a retired teacher in Baghdad and a Palestinian mayor in the West Bank.
Mr. Obama "has to walk the talk," said social activist Marina Mahathir, daughter of Malaysia's former prime minister, Mahathir Mohamad.
But with rising hopes come the risk of disappointment. Mr. Obama isn't expected to present a detailed vision of a Mideast peace deal - potentially the most effective antidote to anti-Western sentiment - until later.
And there is doubt the U.S. president can change entrenched foreign policy, particularly what is perceived in the Muslim world as Washington's pro-Israeli bias. What Muslims see as America's repeated failure to hold Israel to its international obligations is a sore point. A construction freeze in Israeli West Bank settlements - Mr. Obama wants it, Israel rejects it - is shaping up as a major test.
"It's true that Obama's election created a new wave of hope," said Jordan-based political analyst Mouin Rabbani. "But if he pulls the same tricks as his predecessor - making some nice statements and doing the opposite in practice - people will be disabused of their illusions quite quickly."
Mr. Obama will also go to Saudi Arabia and meet King Abdullah on his Mideast trip. But he is not visiting Israel, though just a short flight away.
The president's initial actions have earned him good will. He's reached out to Muslims in an interview with an Arab satellite TV station, in a video message to Iranians on the Persian new year and in a speech to the Turkish parliament. He ordered Guantanamo prison closed within a year and said the U.S. would not engage in torture, reversing two Bush policies seen here as having targeted Muslims.
After the Bush years, one of the darkest periods in U.S.-Muslim relations, there is now a chance for reconciliation, said Shibley Telhami, a Mideast scholar at the University of Maryland who conducts annual public opinion surveys around the Middle East.
"The most striking is the openness toward President Obama and the expressed hopefulness about American foreign policy, something profoundly new, given the last eight years," he said.
In the latest survey, 73 percent of 4,087 respondents felt positive or neutral toward Mr. Obama. The poll had margins of error ranging from 3.6 to 4.5 percentage points, in the six Arab countries where it was conducted in April and May.
The positive results for Mr. Obama seem remarkable for a region where four in five people still hold unfavorable views of the U.S., and Venezuela's stridently anti-American President Hugo Chavez was named most admired foreign leader.
If Mr. Obama wants to rally Muslim support to rein in Iran, analysts say, he will have to prove his good intentions elsewhere. In particular, he needs to move to end Israel's occupation of the West Bank, Gaza and east Jerusalem, lands the Palestinians want for a state.
"If he wants to win the hearts of Muslims, then there must be peace for all of the Middle East," said M. Salim Abdullah, 78, a Muslim of Bosnian descent who heads an Islamic research library in Soest, Germany.
A pullout of U.S. troops from Iraq according to schedule would also go a long way toward restoring Muslim confidence. But despite Mr. Obama's timetable - he plans to withdraw most U.S. troops by September 2010 and pull all out by the end of 2011 - many are upset by the ongoing violence and fear Iraq could one day disintegrate.
Mr. Obama's choice of Cairo as the venue for his speech highlights problems that have long fed militancy in the Arab world. Authoritarian rule, poverty and a lack of opportunity deprive many of the young of a say in their future.
Youth unemployment in the Middle East and North Africa is the highest in the world, with one in four young Egyptians sitting idle, the U.N. says. Nearly 20 percent of Egypt's 79 million people live on less than $2 a day. Islamic militants from Egypt, including al Qaida's No. 2, Ayman al-Zawahiri, have exported their violent ideology. Egyptian President Hosni Mubarak, like other U.S. allies in the region, tolerates little opposition.
Mr. Obama will have to strike a balance between raising human rights violations in Egypt and elsewhere in the region, while not sounding like he is trying to impose U.S. values. The Bush administration's pro-democracy campaign in the Middle East was widely seen as hypocritical, particularly after the U.S. refused to deal with the Islamic militant Hamas despite its 2006 election victory in the Palestinian territories.
"When someone talks to me with dignity and respect, then I will feel I could follow him," said 19-year-old Mustafa Ragab. He spoke after Friday prayers at a Cairo mosque, where the preacher promoted the idea of dialogue ahead of Mr. Obama's visit. "I think Obama will be able to make the Arabs feel that way."
Beyond shared concerns, different parts of the Muslim world have particular issues.
While the U.S. draws down forces in Iraq, it is building them up in another Muslim country, Afghanistan, as part of its intensifying war on the Taliban. But the Afghan government says mounting civilian deaths are undermining support for the campaign.
Kabul shopkeeper Abdul Wasi, 34, said sending more U.S. troops is futile. "The experience of our three decades of war shows that in the end, it will not work," said Wasi, 34. "Since Obama came in, nothing has changed for us."
Iranians say they want Mr. Obama to ease economic sanctions, in place since 1995, and push for a resumption of ties.
"The sanctions the U.S has imposed so far have only damaged ordinary people in Iran," said Tehran mechanic Abbas Taghizadeh.
Millions of Muslims in Europe struggle to win acceptance and shed the stigma of extremism, without sacrificing their customs. They have fought for the right to build mosques and have girls wear headscarves in schools, a sign of religious observance. Mr. Obama may not have much to offer in their struggles.
Still Mr. Obama gets some credit up front for just being himself. Many were inspired by his victory, emotionally connecting to his African and Muslim roots and his childhood in Indonesia, the world's most populous Muslim nation.
"It's so exciting to have a black man run the entire world," said Awni Shatarat, 45, a clothing store owner in the Palestinian refugee camp of Baqaa in Jordan.