President Obama persuaded 46 countries to sign on to a plan to put the world's nuclear material beyond the reach of terrorists within four years, but the commitments are voluntary, and experts said reaching the goal will be difficult.

After almost a decade of deadlock, the United Nations Conference on Disarmament last week approved a working group to negotiate a treaty banning the production of fissionable material for nuclear weapons and another to discuss preventing an arms race in outer space.

Mohamed ElBaradei, the chief of the International Atomic Energy Agency, said in a speech on Monday that the number of reports of nuclear or radioactive material stolen around the world last year was "disturbingly high."

The United States is headed for a showdown with Russia and China this week over competing international treaties, one banning the production of nuclear materials and the other trying to prevent an arms race in space.

The Bush administration's plan for a "renaissance" in nuclear power may be crimped by tightening world-wide supplies of uranium and a lack of enrichment facilities to turn the uranium into fuel for power plants.

The authors propose the establishment of an International Nuclear Fuel Bank, controlled by the International Atomic Energy Agency. Countries would be able to draw fuel for their power plants, provided they agree to strict verification and inspections, and then return the spent fuel for safe oversight by the agency.

Eric Hundman surveys the history of the Global Threat Reduction Initiative and finds that while progress has been slower than expected, the program has "has focused attention worldwide on nuclear security and conversion programs."

Four years after the leaders of the world's eight largest economies vowed to raise $20 billion over 10 years to prevent terrorists from obtaining nuclear materials, only $3.5 billion has been donated -- and far less has been used to secure enriched uranium, the key ingredient of a nuclear weapon.

The Bush administration's plan to deploy a high-tech fuel to power a new generation of nuclear reactors worldwide has a potentially explosive problem: It is too easy for terrorists to grab and turn it into a nuclear bomb.

The Bush administration is preparing a plan to expand civilian nuclear energy at home and abroad while taking spent fuel from foreign countries and reprocessing it, in a break with decades of U.S. policy, according to U.S. and foreign officials briefed on the initiative.