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The 189 treaty members gather every five years to discuss new approaches to problems, by agreeing, for example, that the International Atomic Energy Agency, the U.N. nuclear inspection agency, should be strengthened. The only countries that are not treaty members are India, Pakistan, North Korea — all of which have nuclear arsenals or weapons programs — and Israel, which has an unacknowledged nuclear arsenal.

But the NPT conference cannot easily “name and shame” an alleged treaty violator, such as Iran, since as a member state its delegation would block consensus.

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.

Mr. Obama has steered the United States back onto a negotiating track, including with a new U.S.-Russian agreement to reduce their thousands of long-range nuclear arms.

Despite that, Libran N. Cabactulan, the Philippine diplomat who is president of this 2010 NPT conference, 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.

In his opening remarks, the Mr. Ban listed “real gains for disarmament” as his first “benchmark for success.”

To that end, the Nonaligned Movement of 118 developing nations has submitted to the conference a detailed “plan of action” for moving toward global nuclear disarmament by 2030. One its earliest steps is full ratification and entry into force of the 1996 treaty banning all nuclear tests.

In the first concrete step associated with this 2010 meeting, Indonesia announced last week it would ratify the test-ban treaty. Mr. Obama has pledged to push for U.S. ratification of the pact, which was rejected by the Republican majority in the U.S. Senate in 1999.