President Obama, center, speaks during an International Civil Society event with Tsakhia Elbegdorj, president of Mongolia, left, and Jan Eliasson, deputy secretary-general of the United Nations, on Monday in New York. (Jin Lee/Bloomberg)

For the first time in his presidency, Barack Obama will use his annual visit to the United Nations to manage the most pressing set of foreign policy issues before him, focusing his address and diplomatic energy on the crisis in Syria and on Iran’s nuclear program this week.

Obama has in the past used the annual forum of the U.N. General Assembly to define America’s place in the world — from his first, course-correction speech in 2009 to last year’s defense of U.S. values in the weeks after the deadly attack on U.S. outposts in Benghazi, Libya.

This year, his senior advisers say, the president will focus more tightly on developments in the Middle East, most notably in Syria, where more than 100,000 people are estimated to have been killed in 21 / 2 years of conflict. Obama will call for broader regional engagement to end the Syrian civil war and build upon President Bashar al-Assad’s recent agreement to give up his chemical weapons program after the threat of a U.S. military strike.

At the same time, the White House appears open to a meeting — or, perhaps, only a handshake — between Obama and Iran’s new president, Hassan Rouhani, who has called for a fresh approach to negotiations over the Islamic republic’s nuclear program. No such meeting has been scheduled, White House officials reiterated Monday.

The more-directed approach marks a shift from Obama’s previous visits to the General Assembly and reflects the potential for diplomatic progress on two of the administration’s most vexing overseas challenges.

On Background examines reasons for diplomatic optimism surrounding Iranian President Hassan Rouhani's visit to the United States. (The Washington Post)

Obama will address the General Assembly on Tuesday morning against a backdrop of increasing violence and political insecurity in North Africa and the Middle East, a region recast in recent years by popular rebellions and bumpy transitions.

The Obama administration has appeared passive at times in managing the crises, acknowledging a lack of diplomatic leverage in each case. Assad’s recent decision to turn over his chemical weapons under an agreement partly brokered by the United States marked a more hopeful turn in Obama’s ability to shape events in the region.

This week Obama will press Russia, Iran and other nations that have supported Assad to help force his resignation as part of a broader political solution to end Syria’s civil war. But Russian President Vladi­mir Putin’s skepticism about the larger U.S. approach in the region is slowing diplomacy on this front.

The United States, Britain and France had hoped to have a tough proposal to enforce the U.S.-Russia deal on Syrian chemical weapons ready for consideration at the United Nations by Monday. But it was delayed by Russia’s opposition to some of the stricter enforcement and verification measures, according to U.S. and other diplomats.

Specifically, the United States, Britain and France — all permanent members of the Security Council — are pressing for enforcement under the strongest mandate available to the United Nations, which could allow for military force. The United States has said that it does not intend to use that power but that it wants the Security Council to provide maximum flexibility.

“The debate is not about authorizing use of force in the Security Council resolution. It’s about putting reliable procedures in place” to eliminate Syria’s chemical weapons, a senior State Department official said Monday. “Our bar is that it has to be verifiable and accountable.”

The official spoke on the condition of anonymity to discuss the ongoing Security Council negotiations.

Secretary of State John F. Kerry and Russian Foreign Minister Sergei Lavrov will hash out some of the differences during a meeting at the United Nations on Tuesday, but the delay soured U.S. plans for rapid action at the world body to coincide with Obama’s address.

Kerry was also set to meet Tuesday with the head of the U.S.-backed Syrian opposition movement. Later in the week, he will see Lavrov and Lakhdar Brahimi, the joint U.N.-Arab League envoy to Syria.

The goal of the meeting with Brahimi is to set a date for a much-postponed U.S.-Russia peace conference, likely to be held in Geneva, that would bring together members of the Assad government and the Syrian opposition.

Syria dominated other meetings that Kerry held on the sidelines of the U.N. gathering, including talks with British Foreign Secretary William Hague and Turkish Foreign Minister Ahmet Davutoglu on Monday.

Obama arrived here early Monday afternoon and met with Nigerian President Goodluck Jonathan, whom he praised as the kind of democratic leader who is helping change Africa’s political culture.

He then hosted an open seminar on the role of civil society in promoting change around the world — and how to protect such groups from growing threats.

Speaking to reporters traveling with Obama, Benjamin Rhodes, the deputy national security adviser, said, “We have called upon nations like Russia and Iran to acknowledge the fact that Assad cannot regain legitimacy after slaughtering his people.”

Russia, a veto-holding member of the Security Council, has resisted U.S. demands that Assad step down as part of any peace process. Rhodes said Monday that the administration would not drop that demand.

“It’s an issue that we are going to redouble our efforts onto, not just here at the U.N., but going forward,” Rhodes said.