UNITED NATIONS — It is crunch time for members of the Nuclear Non-Proliferation Treaty, and if their month-long parley here collapses in the next few days it might well be the fault of Egypt, which earlier in the month of May emerged as the darling of advocates for a nuclear-free world.

The Arab countries, led by Egypt and Syria, are agitating to convene a Middle Eastern regional parley within the next two years with the aim of forcing Israel to join the NPT and open its nuclear facilities to international inspection. Western countries say such a conference will be successful only if it also rids the Middle East of chemical and biological weapons.

Syria is suspected of possessing large caches of sarin gas and other chemical and biological arms. Egypt was the first country in the region to have used chemical weapons, in 1964 in the Yemen war, which pitted Soviet-backed locals against Western allies in a classic Cold War era flashpoint. Both countries declined to join the international conventions on chemical and biological weapons.

Without changing their policies on those treaties, Cairo and Damascus in early May initiated the proposal to convene a 2012 regional conference that would discuss the creation of a nuclear-free zone, trying to single out Israel, the only country in the region that has not signed the NPT and kept its atomic weapons program secret while clinging to a policy of nuclear ambiguity. Egypt, however, opposes discussing other WMDs in such a conference.

“We might agree to mention those other types of weapons in the future, but nuclear first. This conference must deal only with nuclear weapons,” an Arab diplomat told me today, as NPT members met for a highly contentious closed-door session.

A Western diplomat noted that the outcome document of the 1995 NPT review conference, on which Egypt now bases its call to convene a regional parley, explicitly calls to advance the promotion of a WMD-free zone.

“Obviously, the last week” of the NPT conference “is when the drama occurs and I don’t want to preempt it, but suffice it say, we’re working hard with others to try and conclude this conference successfully and I’m hopeful that will be the case,” the American ambassador here, Susan Rice, told me today.

Western and Arab diplomats say the conference, which is scheduled to wind down Friday, will end without a signed pact, unless all members agree on the Middle East issue. Such a collapse will resemble the last two times the treaty’s signatories met, in 2000 and 2005. But the Obama administration, which has emphasized its ability to promote international cooperation, is trying hard to avoid comparisons to its predecessor.

The Bush administration declined to negotiate any document that would single out Israel and force it to change its nuclear ambiguity policy. The Obama administration, however, agreed to negotiate with Egypt and the rest of the Arab group over their idea to convene a nuclear conference within the next two years.

As negotiations progressed, disagreements between Arabs and their American and European colleagues have grown, both about substance and format.

In one contention, Arabs want the proposed conference to be convened by the secretary general of the United Nations and force all countries in the region to participate, while Western diplomats lean toward a format that would resemble the 1991 Madrid conference, which was presided over by America and the Soviet Union, and was convened only after all members agreed to come. In another, the West is calling to link the weapons-free zone to progress in peace talks between Israel and the Arabs.

Israel has avoided even hinting at its position on the issue. As a non NPT member, it has conspicuously been absent from the corridors here, where tense negotiations take place daily. According to Israeli press reports President Obama at first accepted the idea of a regional meeting to promote a weapons free zone, but has cooled off since, even secretly telling Prime Minister Netanyahu that Israel will not be forced to join such an international meeting.

Meanwhile, according to diplomats familiar with the internal discussions here, the Arab group itself is split. Saudi Arabia, Jordan, and other American allies are trying to accommodate the West, while Egypt — and even more so Syria — is toughening its stance. Egypt, one such diplomat said, is now secretly hoping that its own initiative will collapse. Syria is working on behalf of Iran, which, according to the diplomat, wants to avoid any talk of a conference that would force it to sit across the table from Israel.