"We think there will be a substantial majority" for such a resolution when the 35-nation board of governors of the International Atomic Energy Agency (IAEA) meets Thursday in Vienna, a Western diplomat said.
Iran, which denies it is trying to develop nuclear weaons, reacted strongly against the possibility of a deadline, as well as the draft resolution's call for it to cease its enrichment activities.
In Tehran, Foreign Minister Kamal Kharazi denounced the "arrogance" and "extremist posture" of certain countries over Iran's nuclear program and warned Tehran might reconsider its cooperation with the Vienna-based IAEA.
The Western diplomats said the 15 co-sponsors of the resolution calling on Iran to reveal by the end of October controversial details about its nuclear program, such as whether it is enriching uranium to weapons-grade level, felt they had a majority of 20 to 22 nations.
The co-sponsors include the United States, Germany, Britain, France and Japan.
These countries held informal talks Wednesday evening with hold-out IAEA members, particularly Russia and non-aligned countries led by Malaysia which want a softer resolution without a deadline, ahead of the board's plenary session Thursday, the diplomat said. The IAEA board has been meeting in Vienna since Monday.
The US ambassador to the IAEA, Ken Brill, said: "What the board members are being called on right now to do is to strengthen the hand of the agency as it seeks to pursue its safeguards responsibilties in support of the" nuclear Non-proliferation Treaty (NPT).
Washington claims Tehran is hiding a program to develop atomic weapons. US President George W. Bush has identified Iran as part of an "axis of evil" of countries trying to manufacture weapons of mass destruction that included then Saddam-ruled Iraq and North Korea.
A Western diplomat said: "I think everybody's very concerned about Iran and one of the reasons why they're concerned particularly in Europe is because there are missiles associated with this."
IAEA chief Mohamed ElBaradei had said Wednesday that he thought "there is broad agreement the (IAEA) would like to see a deadline by which Iran should present all the information (on its nuclear activities) we need to have in order to bring this issue to closure."
ElBaradei told the board that at stake was declaring Iran in non-compliance with the NPT, a step which could bring the issue before the UN Security Council.
ElBaradei said that if Iran had not provided the requested information on uranium enrichment and other matters by the proposed October 31 deadline, then he might have to tell the board he was "not able to verify non-diversion" of nuclear material away from peaceful uses, a Western diplomat said.
The buzz words "non-diversion" are the same as those used in February when North Korea was declared by the IAEA to be in violation of international safeguard agreements.
The United States on Tuesday had accused Iran of being in breach of safeguards agreements from the nuclear non-proliferation treaty but supported a proposed "last chance" for Tehran to clear up questions about its atomic program.
The draft resolution also calls on Iran to sign an additional protocol to allow IAEA inspectors to make unannounced visits to suspect sites.