More than 120 world leaders meet Wednesday on the heels of a climate change summit to tackle other crucial issues on the international agenda from terrorism and the spread of nuclear weapons to growing poverty resulting from the global financial crisis.
"Amid many crises - food, energy, recession and pandemic flu, hitting all at once - the world looks to us for answers," UN Secretary-General Ban Ki-moon said in prepared remarks for the opening of the General Assembly's 64th ministerial session.
"If ever there were a time to act in a spirit of renewed multilateralism, a moment to create a United Nations of genuine collective action, it is now."
A host of new faces will step to the podium at this last General Assembly ministerial session in the UN's landmark headquarters before it closes for renovation later this fall - US President Barack Obama, Russian President Dmitry Medvedev, China's President Hu Jintao and Japan's newly elected Prime Minister Yukio Hatoyama.
A day after some 100 heads of state and government, in the largest-ever summit on global warming, exchanged views on how to reach a new global accord to combat climate change, Ban will again exhort the leaders to "rise to the greatest challenge we face as a human family."
The UN chief will also urge leaders to take steps to free the world of nuclear weapons, to address the "red flags of warning" about a global economic recovery and make a fresh push to achieve UN anti-poverty goals especially reducing maternal and child mortality rates which remain very high, according to his prepared text.
Ban will call for a revival of negotiations to achieve a comprehensive settlement in the Mideast and a two-state solution where Israel and Palestine live side-by-side in peace. And he will pledge to see the Afghans "through their long night" and stand as well with the people of Pakistan.
Security around the sprawling UN complex and adjacent neighborhood is exceedingly tight because of the VIP participants, especially Obama who spoke at Monday's climate summit and will be back in the assembly chamber Wednesday morning to address ministers and diplomats from the 191 other UN member states.
Diplomats said the new US president is almost certain to receive a standing ovation because of the new American commitment to working with countries rich and poor, large and small, to solve global problems and Obama's outreach to the Muslim world.
On Tuesday - in addition to focusing on reducing US carbon emissions, a Mideast summit with the Palestinian and Israeli leaders and a meeting with China's president - Obama invited 25 African leaders and African Union Commissioner Jean Ping to lunch to discuss job creation, particularly for young people, increasing trade and investment and improving agricultural productivity.
Obama stressed that the lunch was not a one-off event but the start of a dialogue between his administration and African leaders, said Michelle Gavin, special assistant to the president and senior director for African affairs. She said she was certain that Obama - whose late father was Kenyan - would make a return visit to Africa "at some point," noting that he has received many invitations.
The US president will chair a high-level meeting of the UN Security Council Thursday on disarmament and efforts to halt the spread of nuclear weapons and the leaders of the four other nuclear powers on the council will also speak - Medvedev, Hu, French President Nicolas Sarkozy and British Prime Minister Gordon Brown.
The council is expected to adopt a resolution calling for stepped up disarmament efforts and a more intense global campaign to reduce nuclear dangers and threats of proliferation. It doesn't name any countries but the draft resolution does refer to previous council resolutions that imposed sanctions on Iran and North Korea for their nuclear pursuits.
Foreign ministers from the five permanent council nations and Germany, who have been trying to curb Iran's nuclear ambitions, will meet with the European Union's top negotiator on Wednesday to discuss prospects and expectations for lower-level talks with Iranian officials on Oct. 1.
Demonstrators have announced protests against two heads of government: Libyan leader Moammar Gadhafi who will be making his first UN appearance after 40 years as ruler of the oil-rich North African nation, and Iranian President Mahmoud Ahmadinejad.
There has been much speculation on whether Obama will cross paths with Gadhafi and Ahmadinejad.
They are all invited to a lunch Wednesday hosted by Secretary-General Ban Ki-moon and then there is a group photo session. Gadhafi is almost certain to meet the US leader if he attends Thursday's Security Council meeting on nuclear nonproliferation to represent Libya, which is a non-permanent council member.
There are many other meetings scheduled on the sidelines of the General Assembly.
Countries concerned with Myanmar, Pakistan and Afghanistan will hold closed-door talks. There will be commemorations of the 60th anniversary of the U.N. agency that deals with Palestinian refugees and of the Geneva Conventions. And there will be a two-day meeting starting Thursday to press for ratification of the nuclear test ban treaty, to name a few.
Ban called in the draft of his speech for urgent support to achieve broad stability in Sudan. He again called for the release of Myanmar's pro-democracy leader Aung San Suu Kyi and for fresh efforts to stop the bloodshed in Gaza.
And he urged all nations to take risks and "rise to an exceptional moment."