The presence of Iran's President Mahmoud Ahmadinejad, the only head of state taking part, ensures sharp words will fly over Tehran's nuclear program and Israel's secret bombs, as well as over treaty outsider North Korea and the huge U.S. and Russian nuclear arsenals.
Departing Tehran on Sunday, Ahmadinejad signaled he'll use the Nuclear Nonproliferation Treaty (NPT) review conference to assail the U.S. and other nuclear-weapons powers for slow movement toward disarmament.
"The atomic bomb has become a tool for bullying, domination and expansionism of some countries and governments," he told reporters.
U.S. Secretary of State Hillary Rodham Clinton, on NBC's "Meet the Press," suggested the Iranian leader was coming to New York "to try to divert attention and confuse the issue," which she identified as Iran's suspected nuclear bomb program, target of U.S.-led efforts to impose a new round of U.N. Security Council sanctions on Tehran.
"We're not going to permit Iran to try to change the story from their failure to comply" with the NPT, she said.
Despite such exchanges, the U.N. conference's Filipino president put the monthlong talks in a more amiable light.
"It's like a recommitment of marriage vows to the treaty, as the cornerstone of nuclear disarmament, nonproliferation and peaceful uses of nuclear energy," said Ambassador Libran N. Cabactulan.
The NPT is the world's single most important pact on nuclear arms, credited with preventing their spread to dozens of nations since entering into force in 1970.
It has done it via a grand global bargain: Nations without nuclear weapons committed not to acquire them; those with them committed to move toward their elimination; and all endorsed everyone's right to develop peaceful nuclear energy.
Treaty members - every nation but India, Pakistan, Israel and North Korea - gather every five years to review how it's working and agree on new approaches to problems. They do that not by updating the treaty, a difficult task, but by trying to adopt a consensus final document calling for steps outside the treaty to advance its goals - in U.S.-Russian arms reductions, for example, or by strengthening the hand of the U.N. nuclear inspectors, the International Atomic Energy Agency (IAEA).
At three of seven past conferences, delegates failed to produce a declaration, including in 2005, at a time when the U.S. administration, under President George W. Bush, was unenthusiastic about arms control talks.
President Obama has steered the U.S. back onto a negotiating track, including with a new U.S.-Russian agreement to reduce their thousands of long-range nuclear arms. Despite that, conference chief Cabactulan said he finds the No. 1 goal of many treaty nations is to press the NPT nuclear powers - also including Britain, France and China - to move more rapidly toward disarmament.
A broad disarmament plan "is both doable and realistic," he told The Associated Press.
"It may not include a definite time in the future for `nuclear zero,"' he said, but it should include, for example, some "clear guideline" for when the treaty banning all nuclear tests should come into force.
The long-languishing test-ban treaty, backed by Obama, faces a struggle for U.S. Senate ratification against Republican opposition.
The "No. 2 challenge" Cabactulan sees in this month's talks is achieving progress toward establishing the Middle East as a zone free of nuclear weapons.
The 1995 NPT Review Conference adopted this as a goal, a concession by the U.S. and others to the Arabs, who want Israel to join the treaty and give up its unacknowledged arsenal of perhaps 80 nuclear weapons. In exchange, the Arabs in 1995 backed permanent extension of the NPT.
After 15 years of inaction on a Mideast no-nuke zone, Egypt has proposed that the 2010 conference endorse launching such negotiations next year. And that could have an indirect, drawn-out effect on one big problem under the NPT, the suspicion that Iran's nuclear power program is aimed at building bombs.
The NPT conference cannot "name and shame" Iran in a final document because, as a treaty member, the Tehran government would block consensus. But Iran has repeatedly endorsed the idea of making its region nuclear weapon-free, in effect trading its presumed weapons-making potential for Israel's decades-old clandestine bomb stockpile.
Ahmadinejad can be expected to repeat that call when he addresses the conference Monday morning, as well as to defend Iran's nuclear program as purely a civilian power project and to denounce U.S.-led efforts to impose new U.N. sanctions on Tehran for refusing to halt uranium enrichment.
Less certain is whether Secretary of State Clinton, speaking for the U.S. later Monday, will also touch on the sensitive subject of Israel's nuclear weapons.
Washington has backed the notion of a "nuke-free" Mideast in the past. "We understand the importance of this issue to this review conference," Susan Burk, chief U.S. NPT representative, said earlier this year. But whether U.S. support in principle translates into backing for specific proposals for action remains to be seen.
While Israel doesn't officially acknowledge its arsenal, its defenders at home and in the U.S. say it needs the bombs as a deterrent as long as much of the Mideast remains hostile to its existence.