JIM LEHRER: President Obama played host to dozens of his counterparts today at a world summit. They focused on stopping the spread of nuclear weapons.
Jeffrey Brown begins our coverage.
JEFFREY BROWN: It's the largest gathering of world leaders ever held in Washington. And, today, President Obama greeted dignitaries from 47 countries, on hand for a two-day summit centered on preventing nuclear terrorism, which the president has called the most immediate and extreme threat to global security.
The gathering here at Washington's Convention Center is intended to focus the world's attention and push countries to take concrete steps to secure the materials that go into making weapons. It's also part of a broader burst of nuclear diplomacy the administration is now engaged in.
Just last week, the president traveled to Prague to sign a new START treaty with Russia that would cut each nation's stockpile of nuclear warheads by nearly a third. That came days after the administration unveiled its nuclear posture review.
ROBERT GATES, U.S. secretary of defense: This review describes how the United States will reduce the role and numbers of nuclear weapons, with a long-term goal of a nuclear-free world.
JEFFREY BROWN: Yesterday and today, the president held a series of bilateral meetings with leaders to address nuclear materials and other issues not necessarily on the summit agenda, but on everyone's minds, including, of course, Iran.
MAHMOUD AHMADINEJAD, Iranian president (through translator): There is no obstacle ahead of our scientists when it comes to nuclear science.
JEFFREY BROWN: On Friday, Iran's President Mahmoud Ahmadinejad unveiled a new generation of centrifuges for enriching uranium.
And while Iran has long maintained its nuclear programs are for peaceful energy generation, the Obama administration has pushed for tough sanctions to keep it from building nuclear weapons, something that key players, notably China, have resisted.
This afternoon, President Obama and Chinese President Hu Jintao discussed the issue, and, according to officials, agreed to increase pressure on Iran. No details were offered.
Iran's nuclear ambitions also play into broader fears some summit attendees have about a new arms buildup in the Middle East. Israel has long been understood to have nuclear weapons, though it maintains an official policy of ambiguity, long a sticking point in the region.
Late last week, amid reports Muslim nations might make Israel's nuke program an issue, Israeli Prime Minister Benjamin Netanyahu announced he would send a deputy in his place.
This morning, I spoke to Egyptian Foreign Minister Ahmed Aboul Gheit about growing nuclear tensions in the Mideast.
The experts that we have talked to have raised some concerns about a potential new nuclear arms race, even as President Obama's talking about a nuclear-free world, the potential for a -- a new arms race in places like the Mideast.
AHMED ABOUL GHEIT, Egyptian foreign minister: Absolutely. And...
JEFFREY BROWN: You worry about that?
AHMED ABOUL GHEIT: Very much so. So, you will have two states, one on the west wing of the Arab world, the other on the east, Iran, Israel. And you have a large community of Arab states that would feel threatened of the presence of two nuclear states.
JEFFREY BROWN: But might that push a nation such -- might that push Egypt to feel that it must develop its own nuclear weapons?
AHMED ABOUL GHEIT: We will not announce ourselves on that possibility now. But we would really feel concerned to have a Middle East that is -- that is facing that potential, the proliferation. We have to act, and to act today, not tomorrow or the day after.
JEFFREY BROWN: The president's goal is to act soon, at least in securing stores of highly enriched uranium and plutonium found in thousands of sites around the world, in countries like Pakistan, with its relatively new nuclear arsenal and others that have current or aging nuclear energy programs, even if they don't produce weapons.
The administration announced a deal today with Ukraine to remove its stockpile of uranium, enough, it is said, to build several nuclear weapons.
Gary Samore is a White House adviser on arms control.
GARY SAMORE, presidential adviser on arms control: ... that the steps we're taking here will have a concrete consequence in terms of locking down material, increasing cooperation against nuclear smuggling, and therefore making nuclear terrorism less likely.
SHARON SQUASSONI, proliferation prevention program director, Center for Strategic and International Studies: Terrorists are definitely interested in acquiring either weapons or material.
JEFFREY BROWN: Sharon Squassoni is with the Center for Strategic and International Studies.
SHARON SQUASSONI: The nuclear security summit tries to say, hey, there's no big difference between the nuclear weapons states and the non-nuclear weapons states. Nuclear security affects us all. We all need to take steps to ensure that terrorists don't get access to nuclear material.
So, in a way, it's going to play this role to bring greater cohesion among wide varieties of states.
JEFFREY BROWN: But Henry Sokolski of the Nonproliferation Policy Education Center says the very different situations among the many nations pose limits to what the U.S. can ask.
HENRY SOKOLSKI, executive director, Nonproliferation Policy Education Center: When you get into the specifics of what they need to do to secure their material, you eventually run up against their desire not to give you too much information about where their material is, and your desire not to reveal what exactly your procedures are for protecting your material, lest someone figure out how to defeat it. So, there's a natural limit to how far we can go.
JEFFREY BROWN: The full summit gets under way tonight with a working dinner. Tomorrow, delegates will hold a series of plenary meetings, which the administration hopes will yield agreement on securing nuclear materials worldwide.