But Iran remains defiant. In a last-minute warning, Tehran's chief nuclear negotiator told Mohamed ElBaradei, the director general of the UN's International Atomic Energy Agency (IAEA), that his country would severely curtail the agency's inspections of the Islamic republic's atomic programme and resume uranium enrichment if it was reported to the council.
In a letter, Ali Larijani said such a move would leave his country no choice but "to suspend all the voluntary measures and extra cooperation" with the IAEA - in other words, reduce the agency's monitoring authority over its nuclear activities to a minimum.
Furthermore, "all the peaceful nuclear activities being under voluntary suspension would be resumed without any restriction," warns the letter, in an allusion to previous threats to resume work on full-scale uranium enrichment - a possible pathway to nuclear arms.
Mr ElBaradei said that yesterday's IAEA meeting, which was scheduled to continue today, opened up a "window of opportunity" to defuse the crisis, stressing that even if the issue is referred, the Security Council would not take up the topic before next month.
"We are reaching a critical phase but it is not a crisis situation. It's about confidence- building and it is not about an imminent threat," he said.
Intelligence estimates of when Iran might be able to build a bomb range from two to over ten years.
However in Washington, John Negroponte, the US intelligence chief, said the danger of Iran acquiring a nuclear weapon and the ability to add it to ballistic missiles it already possesses was reason "for immediate concern". But Mahmoud Ahmadinejad, the Iranian president, accused the West of "arrogance" in seeking Security Council engagement in restraining Iran's quest for nuclear energy.
"[You] have got nerve to try to deprive us of our legal right ... Who are you to threaten our nation like that? The Iranian nation is aware of your plots and will not be deceived by you and will stand against your excessive demands," he said.
Iran concealed nuclear activities from the IAEA for 18 years until 2003. In September, the IAEA declared Iran non-compliant with its commitments as a party to the nuclear Non-Proliferation Treaty, but put off referring it to the Security Council.
US and European diplomats intensified efforts to reach broad agreement on a referral ahead of a decision by the IAEA's 35- nation board of governors.
Diplomats at the meeting said this appeared certain, but Washington and the EU, the key backers of referral, wanted to build as much support as possible.
The IAEA board was expected to approve the motion easily because Russia and China - which have veto power on the Security Council along with the US, Britain and France - now support reporting Iran, following months of opposition.
Iran insists its nuclear programme is peaceful and aimed only at generating electricity, but key permanent members of the Security Council remained unmoved.
Grigory Berdennikov, Russia's chief IAEA delegate, reinforced Moscow's position outside the meeting, telling reporters that referral to the Security Council would send Iran "a serious signal".
And the top US delegate agreed: "It is time to send a clear and unequivocal message to the Iranian regime about the concerns of the international community by reporting this issue to the Security Council."
Only a simple majority is needed to approve the text of a referral to the Security Council. While a broad majority of member nations support referral, a handful of countries that have major policy disputes with the US remain opposed - among them Cuba, Venezuela, Syria and Belarus.
"My delegation manifests its total disagreement with the proposal... to bring it to the Security Council," said the Venezuelan delegate.
A vote could be held today or tomorrow, as diplomats said the draft could still undergo small modifications to gain more support.
Diplomats said India, which had been opposed, was leaning toward supporting the draft now that China and Russia had signed up to it.
Countries opposed have the choice of directly voting against the text or abstaining.
Speaking for Germany, Britain and France - the three nations representing the EU - the German delegate told the meeting: "The time now has come for the Security Council to get involved."
Iran's decision on 10 January to restart small-scale uranium enrichment - and Mr Ahmadinejad's recent calls for Israel to be "wiped off the map" - apparently rattled Beijing and Moscow enough to support the US position.
If the board approves referral, as expected, it will launch a protracted process that could end in Security Council sanctions for Tehran.
Moscow and Beijing support referral only on condition that the council take no action until at least March.
Speaking in Washington, Mr Negroponte, the US national director of intelligence, said: "We judge that Tehran probably does not yet have a nuclear weapon and probably has not yet produced or acquired the necessary fissile material."
However, he added: "The danger that it will acquire a nuclear weapon and the ability to integrate it with the ballistic missiles Iran already possesses is a reason for immediate concern." Mr Negroponte also told a US Senate intelligence committee that al-Qaeda is still plotting and preparing for attacks on the United States.
He said that although much of al-Qaeda's leadership has been eliminated, its "core elements still plot and make preparations for terrorist strikes against the [US] homeland and other targets from bases in the Pakistan-Afghanistan border area".
"The group will attempt high-impact attacks for as long as its central command structure is functioning and affiliated groups are capable of furthering its interests, because even modest operational capabilities can yield a deadly and damaging attack," he said.
An attack using conventional explosives remains the "most probable scenario," but al-Qaeda remained interested in acquiring chemical, biological, radiological and nuclear materials or weapons, he said.