The single greatest danger facing humanity, President Bush (search) says, is the threat of nuclear weapons falling into terrorist hands.

So in the next four years, Bush looks to work with other nations to prevent countries from developing nuclear weapons, to secure and dismantle weapons that already exist and stop black-market trafficking of nuclear materials.

This isn't exactly the arms control of past presidents — the lengthy negotiations and detailed agreements, mostly between the United States and the Soviet Union or Russia over nuclear stockpiles, missile defense and weapons testing.

Instead, this is arms control rooted in the Sept. 11, 2001 (search), attacks.

"Those attacks also raised the prospect of even worse dangers — of other weapons in the hands of other men," Bush said in February. "The greatest threat before humanity today is the possibility of secret and sudden attack with chemical or biological or radiological or nuclear weapons (search)."

Bush has said terrorism is a global problem and he's looking for a multinational solution. He has worked with other nations to stop North Korea and Iran from developing nuclear programs. He has promoted new programs to encourage countries to intercept weapons components and to help nations secure or remove radioactive materials.

He has also promised to expand on the 1991 Nunn-Lugar program for dismantling weapons of mass destruction in the former Soviet Union and finding work for former weapons scientists.

The program's co-founder, Sen. Richard Lugar, R-Ind., said he will propose legislation this week to eliminate bureaucratic snags and to create a new program aimed at dismantling conventional weapons. He said he has worked with the administration on the plans.

But Democrats and some analysts say the president's efforts don't reflect the urgency of the threat. And they say his ability to rally nations behind his arms control measure has been undermined by his disdain for older weapons treaties and the faulty U.S. intelligence on Iraq's weapons programs.

Jack Mendelsohn, a U.S. arms control negotiator in the 1970s and '80s, said U.S. credibility on identifying nuclear threats "is only slightly greater than zero" because of Iraq.

When the United States describes dangers in Iran or North Korea's nuclear programs, "the other countries say, `Yeah, but you guys tend to go off the deep end and you exaggerate,"' he said.

But to the administration, the threats from both nations are real. They are the two remaining points on Bush's "axis of evil" now that Iraq's Saddam Hussein has been toppled, and both are considered sponsors of terrorism.

The United States is working with South Korea, China, Russia and Japan in talks aimed at ending North Korea's nuclear weapon program. It is looking for France, Germany and Britain to persuade Iran to indefinitely suspend its uranium enrichment program. If no agreement is reached, the United States wants the U.N. Security Council to consider sanctions. Iran says its nuclear program is only for generating electricity.

To prevent problems similar to those in Iran, the administration is seeking support for protocols to the Nuclear Nonproliferation Treaty to make it harder for countries to use nuclear energy programs as a cover for weapons production.

Bush has shown less interest in traditional arms treaties. The one major agreement he signed with Russia, the Moscow Treaty, called for a two-thirds reduction in strategic nuclear warheads by 2012. But it requires weapons only to be removed from service, not destroyed, and either side could easily withdraw.

Bush withdrew the United States from the 1972 Anti-Ballistic Missile treaty and is working on a limited missile defense system. He opposes the Comprehensive Test Ban Treaty, which was never ratified by the Senate. Although his administration hasn't conducted tests, it has worked to speed up the time needed for tests to be conducted. He has also pushed for research on new types of nuclear weapons.

Some analysts say the president's rejection of older arms-control efforts will make it harder for him to persuade countries to agree to his nonproliferation proposals.

"It gives other countries an excuse," said Jim Goodby, who held various arms control positions from the 1950s to 1990s. "If a country says we would rather not do something that constrains us, all they have to do is point to the U.S. behavior and they can justify it."

Some analysts believe the greatest nuclear threat to the United States could come from Pakistan.

Bush has cited as a success the breakup of a proliferation network headed by Pakistani scientist A.Q. Khan, and President Pervez Musharraf has become an important ally in the fight against terrorism. But Islamic militants are active in Pakistan and its politics are turbulent.

Joseph Cirincione of the Carnegie Endowment for International Peace, said instability in Pakistan could "mean a hemorrhaging of nuclear expertise, materials and possibly even weapons themselves."

"Our policy toward Pakistan is basically the hope that everything stays OK," he said.