United Nations ? Secretary-General Kofi Annan challenged the United States and Russia on Monday 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 guarantees of nuclear fuel.

U.N. Secretary-General Kofi Annan addresses a conference to review the Nuclear Nonproliferation Treaty Monday at the United Nations headquarters in New York. At a time of growing nuclear tensions in the world, U.N. Secretary-General Kofi Annan on Monday urged nonweapons states like Iran to step back from the nuclear temptation, and America and Russia to cut back more sharply on their arsenals.

The U.N. 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. 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 the five nuclear powers — the United States, Russia, Britain, France and China — to move toward 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.