Obama: U.S. Can't Fix the World Alone

Seizing a chance to challenge the world, President Obama says the global community is failing its people and fixing that is not "solely America's endeavor."

"Those who used to chastise America for acting alone in the world cannot now stand by and wait for America to solve the world's problems alone," Obama said in a passage of the speech he was delivering Wednesday to the United Nations General Assembly.

The White House released excerpts in advance that carried a remarkably blunt tone.

It comes in Obama's first speech to this world body, a forum like none other for a leader hoping to wash away any lasting images of U.S. unilateralism under President George W. Bush.

In essence, Obama's message is that he expects plenty in return for reaching out.

"We have sought in word and deed a new era of engagement with the world," Obama said, echoing the cooperative theme he promised as a candidate and has since used as a pillar of his foreign policy. "Now is the time for all of us to take our share of responsibility."

CBS News senior White House correspondent Bill Plante reports that the president will lay out as his top priorities curbing the spread of nuclear weapons, slowing the effects of climate change and stabalizing the global economy.

Obama said if the world is honest with itself, it has fallen woefully short.

"Extremists sowing terror in pockets of the world," Obama said. "Protracted conflicts that grind on and on. Genocide and mass atrocities. More and more nations with nuclear weapons. Melting ice caps and ravaged populations. Persistent poverty and pandemic disease."

The president added, "I say this not to sow fear, but to state a fact: the magnitude of our challenges has yet to be met by the measure of our action."

"This is an opportunity not only to engage and to recommit to the U.N., which he will no doubt do, but to challenge the U.N." to deal with the real problems facing the world, said CBS News analyst Juan Zarate.

Obama's speech is the centerpiece of a dizzying agenda that will also see him holding pivotal meetings with the new Japanese prime minister, Yukio Hatoyama, and Russian President Dmitry Medvedev.

Immersed, Obama foreshadowed his message to world leaders in a speech Tuesday to the Clinton Global Initiative. He spoke of nations interconnected by problems, whether a flu strain or an economic collapse or a drug trade that crosses borders.

"Just as no nation can wall itself off from the world, no one nation - no matter how large, no matter how powerful - can meet these challenges alone," Obama said.

While that point is hardly new, it is sharper because of the political context. Obama follows Bush, who at times questioned the U.N.'s toughness and credibility, particularly in containing Iraq's Saddam Hussein. The U.S.-U.N. relationship wilted.

Obama's team is intent on drawing the contrast.

"The United States has dramatically changed the tone, the substance and the practice of our diplomacy at the United Nations," said Susan Rice, Obama's ambassador to the U.N.

But multilateralism has its limits, particularly as national interests collide.

Obama needs the sway of Russia and China in getting tougher U.N. action against Iran over its potential nuclear weapons program, and neither country is showing interest.

Will Obama and Iran Leader Cross Paths?

While other world leaders could push for Mideast peace, it was Obama who personally intervened in pulling together the Israeli and Palestinian leaders on Tuesday. He showed some impatience as both sides have been stalled over familiar issues.

The good-will feeling of Obama's fresh government is apparent at the United Nations.

But eight months into his presidency, the problems he inherited are now his own, upping expectations for results. His White House is being pressed to right the war in Afghanistan. And his efforts toward diplomacy with adversaries, chiefly Iran and North Korea, are not meant to be open-ended.

Obama's day starts with his meeting with Hatoyama, who has said he wants to shift Japan's diplomatic stance from one that is less centered on Washington's lead.

Later, Obama was meeting with Medvedev. That session comes just days following Obama's decision to abruptly scrap a Bush-era missile defense plan in Eastern Europe that Russia deeply opposed, swapping it for a proposal the U.S. says better targets any launch by Iran.

Watch: New Approach on Missile Defense

Russian leaders rejoiced over Obama's move, but he dismissed any role Russia may have played and called it just a bonus if the country is now less "paranoid" about the U.S.