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In a world of growing nuclear fears and mistrust, U.S. negotiators come to New York on Monday to urge a global nonproliferation conference to take action on Iran and North Korea (search).

But the Americans and other nuclear powers will face demands themselves. Non-nuclear states last week complained the big powers were moving too slowly toward nuclear disarmament, described as "not an option, but a legal obligation" under the Nuclear Nonproliferation Treaty (search).

Because of this clash of priorities, treaty members on Sunday still hadn't completed an agenda for the monthlong conference opening Monday to review the NPT, whose workings are reassessed every five years.

Thousands of protesters made their priorities clear on the eve of the opening, as they marched past the United Nations in blustery New York spring weather. "Abolish nuclear weapons now!" and "No more Hiroshimas," read banners carried by a large Japanese contingent in the anti-nuclear march.

"No nation, no group should test and make material for nuclear weapons. Everything should be banned," said Mayor Tadatoshi Akiba (search) of Hiroshima, the city obliterated by a U.S. atomic bomb in 1945.

In distant capitals, nuclear tensions heightened over the weekend as the U.N. conference neared.

After renewed talks with European negotiators made no reported progress, Iran said Saturday it would probably resume disputed operations this week related to uranium enrichment, a potential step toward an atom bomb.

North Korea, meanwhile, denounced President Bush on Saturday as a "hooligan" and said it doesn't expect a solution to the standoff over its nuclear program during his tenure. The escalating rhetoric was followed Sunday by a test-firing of a North Korean short-range missile into the Sea of Japan.

The North Koreans, who declared in 2003 they were withdrawing from the NPT, have since said they have built nuclear weapons.

Under the 35-year-old NPT, North Korea and 183 other states were to have forsworn such arms in exchange for a pledge by five nuclear powers — the United States, Russia, Britain, France and China — to move toward nuclear disarmament. But, under treaty rules, Pyongyang was able to withdraw without penalty.

Conference organizers anticipate a low-key approach toward North Korea, to avoid complicating efforts to draw it back into six-party talks aimed at shutting down its nuclear program. But Bush administration officials say they will work to make treaty noncompliance the focus of the review sessions.

"The conference should condemn North Korea's egregious behavior," U.S. delegation leader Stephen G. Rademaker told a House subcommittee last Thursday.

Without targeting Pyongyang, European and Canadian proposals before the conference would make it more difficult for future North Koreas to withdraw from the treaty without sanction.

The Iran situation hinges on another part of the NPT "bargain," the treaty's guarantee that nonweapons states have access to peaceful nuclear technology, including uranium-enrichment equipment that can produce fuel for nuclear power plants and, with further enrichment, for nuclear bombs.

The Bush administration says Iran's enrichment program, which was long secret, is meant for weapons-building, a charge Tehran denies.

President Bush proposes banning such sensitive dual-use equipment from all but the United States and a dozen other countries that already have it. Mohamad ElBaradei, head of the U.N. nuclear agency, proposes a less discriminatory approach: putting fuel production under multilateral control, by regional or international bodies.

Neither idea has yet gained wide support, but many conference participants see open access to the nuclear fuel cycle as an NPT loophole. Potential remedies are sure to be discussed.

Iran has countered with a proposal to make the Middle East a nuclear weapons-free zone, which would mean elimination of Israel's arsenal. Israel, India and Pakistan — all with nuclear weapons — remain outside the Nonproliferation Treaty.

Nonweapons states, meanwhile, say they're increasingly frustrated by Bush administration policies — its rejection of the nuclear test-ban treaty, its withdrawal from the antiballistic-missile treaty, and its talk of modifying and developing new nuclear weapons.

An 89-nation meeting in Mexico City last week adopted a preconference declaration expressing "deep concern" over what is seen as moves contrary to the NPT's disarmament clauses.

"Achieving nuclear disarmament is not an option, but a legal obligation contained in the NPT," Mexico's Luis Alfonso de Alba said at the meeting.