The resolution would require all 191 U.N. member states to pass laws to prevent terrorists, black marketeers and other so-called "non-state actors" from buying or selling components for weapons of mass destruction.

The measure is sponsored by the United States and Britain, and supported by the other permanent Security Council members. But at least one other declared nuclear power on the Council, Pakistan, has expressed strong reservations.

Pakistan admitted earlier this year that its most prominent nuclear scientist had smuggled weapons secrets to North Korea, Iran and Libya.

During an open debate last week, Pakistan's ambassador, Munir Akram, asked whether the Security Council should assume the role of requiring member states to pass laws. He also objected to inclusion of the resolution under chapter seven of the U.N. charter, which would allow military enforcement against violators. "There is no justification for the adoption of this resolution under Chapter Seven of the Charter. The threat of WMD proliferation by non-state actors may be real, but it is not imminent. It is not a threat to peace," he said.

Pakistan's concerns were echoed by the Non-Aligned Movement, a group of more than 100 mostly developing countries.

In an attempt to address these objections, U.S. Deputy Ambassador James Cunningham circulated a revised draft resolution this week. During the open debate, he stressed the urgency of the matter. "Terrorist groups such as al-Qaida have shown their willingness to kill thousands and they do not hide their desire to acquire weapons of mass destruction and their means of delivery in order to increase that number many times over. If such a group acquired these weapons, they could be used to bring sudden disaster and suffering on a scale that we can scarcely imagine," he said.

In his speech to the General Assembly last September, President Bush said the WMD resolution was needed to fill a gap in previous weapons treaties. Past accords have addressed the possession of weapons of mass destruction by states, but not by terrorist groups.

The measure is expected to come to a vote as early as Wednesday. It would win approval even without Pakistan's support, since only the Council's five permanent members have veto power.