It was meant to be the centerpiece of UN chief Kofi Annan's ambitious plan to reform the world body on its 60th anniversary.
Enlarging the powerful, 15-member Security Council was supposed to reflect the 21st century's new balance of forces, enshrining the enhanced status of economic powerhouses Germany and Japan -- the World War II losers -- and the emerging power of India and Brazil.
But the plan, which was to have been endorsed by world leaders at their summit this week, has become a victim of the competing egos and interests of rival nations.
Its most promising version came in a draft introduced in the UN General Assembly in July by the so-called G4: Brazil, Germany, India and Japan. It called for boosting council membership to 25, with six new permanent non-veto-wielding seats -- the G4 nations plus two from Africa -- and four non-permanent seats.
The G4 draft was endorsed by nearly 40 nations, including Britain and France, but it also needed the backing of the 53-member African Union to secure the required two-third majority in the 191-member assembly.
The G4, particularly Japan and Germany, mounted an aggressive drive to woo the Africans, who were pressing to correct what they see as a historical injustice that has left them as the only continent not represented on the Security Council.
But the Africans, led by Algeria and Egypt, pushed their own draft calling for two permanent Security Council seats for Africa -- with the right to veto resolutions -- and five non-permanent council seats, including two for Africa.
That demand for veto power was generally viewed as unrealistic as the five current permanent members -- Britain, China, France, Russia and the US -- were unwilling to share their veto right.
Yet as the US and China signaled opposition to the G4 blueprint, the Africans decided at a summit in Addis Ababa last month to reject a compromise deal offered by the G4 and backed by Nigeria, the current AU chairman.
Analysts said the AU stance stemmed in part from rivalry for Africa's two council slots. Regional powerhouses Egypt, Nigeria and South Africa were seen as favorites, but Kenya, Angola, Libya and Senegal also made a claim.
Early on, the US warned it would reject any major expansion of the council, stating its preference for only two additional permanent seats, including one for Japan.
In July, Washington sent Undersecretary of State for Political Affairs Nicholas Burns to the UN to say that a vote on council expansion would be premature and divisive and said they should focus instead on management reform.
China, which had previously backed council seats for Brazil, Germany and India, is against permanent status for regional rival Japan, due to its perceived refusal to face up to its wartime past.
To muddy the waters further, a group led by Canada, Pakistan and Italy pushed its own proposal to enlarge the council from 15 to 25 seats with 10 new non-permanent members elected for two-year terms, with the possibility of immediate re-election.
Each of the G4 aspirants had serious regional opposition: India from Pakistan, Brazil from Argentina and several Latin American countries, Japan from China and South Korea, and Germany from Italy, diplomats said.
But in the end it was the opposition of the Washington and Beijing which sank the G4 bid, diplomats said.