The US says it is likely to back the limited expansion of the UN Security Council, allowing at least two new nations to take up permanent seats.
The structure of the Security Council has not changed since WWII
US Under-Secretary of State Nicholas Burns said none of the new members should have the veto rights currently held by the body's permanent members.
Several nations including Japan, India, Germany and Brazil are campaigning for permanent places on the council.
China, France, Russia, the US and UK currently hold the permanent seats.
The US will put forward a resolution next week at the UN General Assembly setting out its criteria for UN and Security Council reform.
Backing for Japan
Mr Burns said the US will also back adding two or three non-permanent seats to the council.
The council currently has 10 non-permanent seats occupied in rotation by UN member nations.
The BBC's Jonathan Beale says the US proposals to expand the membership fall far short of what many countries have been arguing for.
Japan, India, Brazil and Germany have put forward a plan for adding 10 seats to the council - six of them permanent, including two from Africa, and four of them non-permanent.
Their plan delays veto rights for new members for 15 years.
Washington has said it supports Japan's bid for a permanent seat, which China has opposed.
'One of many issues'
The acting US ambassador to the UN, Anne Patterson, said several criteria had to be considered in assessing whether a nation was fit for permanent council membership.
These included its wealth, population, democratic credentials and its ability to contribute to the UN's finances and peacekeeping operations.
"We don't think geography should be the sole criterion for membership," she said.
Mr Burns said the UN must make progress on several other issues before it turned to the Security Council debate.
"We see this debate as only one of the issues that has to be put forward," he said.
UN Secretary General Kofi Annan has argued for the expansion of the council, which has the power to impose sanctions and to endorse military action.