WASHINGTON -- President Barack Obama persuaded 46 countries Tuesday to sign on to a plan to put the world's nuclear material beyond the reach of terrorists within four years, but the commitments were voluntary, and experts said reaching the goal will be difficult.
The governments attending Obama's Nuclear Security Summit agreed to take their own measures to safeguard nuclear material used in bombs, civilian nuclear reactors and power plants, and to strengthen international efforts.
The gathering raised the profile of an issue long considered a sideshow in discussions of international security.
"This is an ambitious goal, and we are under no illusions it will be easy. But the urgency of the threat and the catastrophic consequences of even a single act of nuclear terrorism demand an effort that is at once bold and pragmatic," Obama said at a news conference.
The summit was part of Obama's "nuclear spring," a broad effort to revive U.S. arms-control efforts and elevate the role of international treaties in U.S. nuclear weapons policy.
The idea is to enhance the standing of the United States as it tries to prevent the world's nonproliferation system from collapsing. A key conference will be held next month on strengthening the Non-Proliferation Treaty, which long has restrained countries' nuclear ambitions but has been flouted in recent years by Iran and North Korea.
David Miliband, the British foreign secretary, said Obama's summit should be seen in a broader context that includes the recent signing of a U.S.-Russia arms-reduction treaty. "What they've done is break a culture of cynicism" about nuclear issues, Miliband said.
One Obama critic questioned whether the gathering of 37 government leaders, as well as delegations from 10 other countries, went far enough.
"The summit's purported accomplishment is a nonbinding communique that largely restates current policy and makes no meaningful progress in dealing with nuclear terrorism threats or the ticking clock represented by Iran's nuclear weapons program," said Sen. Jon Kyl, R-Ariz., a prominent critic of Obama's nuclear policies.
Kenneth Luongo, an expert on nuclear security at the Partnership for Global Security, said Obama "has put his personal prestige on the line like no other world leader has before" on the issue.
The commitments were positive, he said, "but when the lights go down tonight, leaders need to hit the ground running on implementation."
The most obvious result of the summit was a series of pledges, nicknamed "house gifts" by the Obama administration. For example, India declared that it will build a center to promote nuclear security, in what experts called a significant change in its focus on the issue.
Ukraine, Mexico, Chile, Kazakhstan, Vietnam and Canada agreed to dispose of hundreds of pounds of highly enriched uranium used in civilian facilities. The material, a key ingredient in nuclear bombs, often can be replaced for civilian uses with far less dangerous low-enriched uranium.
The Obama administration, for its part, said it recently submitted legislation so Congress will get around to ratifying two international agreements on nuclear material. In addition, Washington will request a security review of a U.S. neutron research center by the International Atomic Energy Agency (IAEA), the U.N. nuclear watchdog.
"We used the summit shamelessly as a forcing event" to get concrete actions, said Gary Samore, the top nuclear official on the National Security Council.
A follow-up meeting to gauge countries' progress is to be held in six months, and another summit in two years.
"You've already seen efforts that had been delayed for years, in some cases since the end of the Cold War, finally come into fruition here at this summit," Obama said.
Still, experts questioned whether it would ever be possible to "lock down" nuclear material completely, noting that there is no uniform standard and no international authority to check on compliance.
Among other challenges, there are still hundreds of civilian research reactors around the world that use highly enriched uranium. Converting them to use low-enriched uranium is expensive.
And some experts raised doubts about whether the IAEA is up to the task of helping ensure nuclear security. The agency's main job is ensuring that countries aren't building atomic bombs, and it has a budget of less than $10 million for the safeguarding of nuclear material worldwide, Luongo said.
The summit avoided the divisive issue of whether countries should extract plutonium from spent fuel from nuclear energy plants. The material can be reused in other reactors but could also be used in bombs.
Henry Sokolski, director of the Nonproliferation Policy Education Center, said that issue could become more important as nuclear power plants multiply. "That's the underlying problem that's not being addressed. It's like you can have your nuclear cake and eat it too," he said.
Samore said an important achievement of the summit was getting commitments from countries that previously had not made a high priority of nuclear security, especially in regions such as Latin America and the Middle East.
As for the lack of enforcement mechanisms, he said countries were reluctant to agree to such measures because of fears that their sovereignty would be violated.
He said French President Nicolas Sarkozy proposed setting up an international court to try officials who spread nuclear materials to terrorists. Obama said the idea "certainly merited further discussion," Samore said. But Washington has been wary of acceding to international courts.
Russian President Dmitry Medvedev, in a post-summit speech at the Brookings Institution, called the gathering "a complete success." But he said there is a lot more work to be done on every level of arms control and nonproliferation. "I hope we won't just go home feeling happy."
Staff writer Karen DeYoung contributed to this report.