UNITED NATIONS -- Secretary-General Kofi Annan challenged the United States and Russia yesterday to slash their nuclear arsenals irreversibly to just hundreds of warheads, and urged nonweapons states like Iran to give up potential bomb technology in return for international guarantees of nuclear fuel.
The UN atomic energy chief followed with an offer to begin work on a system of international fuel supplies.
The two spoke at the opening of a monthlong conference to review the workings of the Nuclear Nonproliferation Treaty, or NPT. The session comes at a time of mounting nuclear tensions over North Korea's withdrawal from the 189-nation pact and Iran's program to enrich uranium, a possible step toward a bomb.
''Developments of many kinds in recent years have placed it under great stress," Annan said of the treaty.
The United States wants the review conference to focus heavily on North Korea, Iran, and the nuclear fuel issue. But many states without nuclear arms want equal emphasis on what they see as a softening commitment by the big powers to nuclear disarmament.
Because of the differing priorities, treaty members were unable to agree on a complete agenda for the conference. Organizers hope to have agreement before the nuts-and-bolts work of committees begins next week.
Under the 35-year-old NPT, states without nuclear arms pledge not to pursue them, in exchange for a commitment by five nuclear powers -- the United States, Russia, Britain, France, and China -- to move toward nuclear disarmament. Three other nuclear states -- Israel, India, and Pakistan -- remain outside the treaty.
The NPT is reviewed every five years at conferences whose consensus political commitments are not legally binding, like a treaty, but give valuable support to nonproliferation initiatives. At the 2000 sessions, the nuclear powers committed to ''13 practical steps" toward disarmament, but critics complain the Bush administration -- by rejecting the nuclear test-ban treaty, for example -- has come up short.
The nuclear powers must find ways to rely less on nuclear deterrence, Annan said in his keynote speech, and he called on Washington and Moscow ''to commit themselves -- irreversibly -- to further cuts in arsenals, so that warheads number in the hundreds, not the thousands."
Under the 2002 Moscow Treaty, the United States and Russia are to cut back their deployed warheads by two-thirds, to between 1,700 and 2,200 each, by 2012. But the agreement has been criticized for not requiring destruction of excess warheads, or providing a transparent timetable and open verification of reductions.
''We are proud to have played a leading role in reducing nuclear arsenals," said Stephen G. Rademaker, an assistant secretary of state.
When the Moscow agreement is implemented, Rademaker said, ''the United States will have reduced the number of strategic nuclear warheads it had deployed in 1990 by about 80 percent." He said the conference should focus instead on Iran and North Korea.
The Iran question hinges on the NPT's Article IV, which guarantees nonweapons states the right to peaceful nuclear technology, including uranium enrichment equipment to produce fuel for nuclear power plants.
That same technology, with further enrichment, can produce material for nuclear bombs, and the United States alleges that's what Iran plans -- a charge Tehran denies.
Annan said states such as Iran ''must not insist" on possessing such sensitive technology, but instead should have access to nuclear fuel.
Following Annan to the UN podium, Mohamed ElBaradei, director-general of the International Atomic Energy Agency, renewed his call for a moratorium on new fuel-cycle facilities while international controls are negotiated.
ElBaradei proposes putting nuclear fuel production under multilateral control by regional or international bodies. Rademaker reaffirmed President Bush's proposal for an outright ban on nuclear fuel technology.
The Tehran government is negotiating on and off with Germany, France, and Britain about shutting down its enrichment operations in return for economic incentives. After the latest round failed to produce agreement Friday, the Iranians said they would probably restart enrichment-related operations this week.
North Korea, which pulled out of the NPT in 2003, said in February it has already built nuclear weapons.