Diplomats in New York have agreed on a draft package of reforms for the historic World Summit due to open at the United Nations on Wednesday.
Kofi Annan had publicly called for major reform of the Security Council
The draft was hammered out after weeks of bitter wrangling and pledges to honour anti-poverty goals, but other points are diluted or omitted entirely.
A meeting of the full, 191-member UN General Assembly later endorsed it.
World leaders are converging for the summit, which celebrates 60 years of the UN as a body.
UN Secretary-General Kofi Annan told reporters the draft document had two important omissions - non-proliferation and disarmament.
"This is a real disgrace," he said, adding that he hoped world leaders would take up the issues up at the summit.
"We didn't get everything we wanted... but we can build on it," he said.
Other proposed reforms which proved contentious were the creation of a new human rights body, the definition of terrorism and UN managerial reform.
Plans to reform and enlarge the 15-member UN Security Council, backed by Mr Annan, were dropped before negotiations on the document even began.
John Bolton, the US ambassador to the UN, said he was pleased with the outcome and added that he had never expected everything to be agreed at this stage.
"This is not the alpha and omega and we never thought it would be," he said.
Jean Ping, the chairman of the General Assembly, came up with a compromise text:
- On the human rights body proposal, the document simply states a pledge to set up a new council, without more details
- A commitment to break down trade barriers was substantially weakened
- Diplomats did agree on the creation of a peace-building commission to help nations emerging from war and on an obligation to intervene when civilians face genocide and war crimes
- A section on development voices support for the UN's Millennium Development Goals, a long-term strategy for eliminating world poverty.
Mr Ping described the document and the United Nations itself as a reflection of the international community.
A spokesman for the UK-based aid agency Oxfam criticised the compromise deal and accused several countries of undermining the deal.
"Leaders will arrive to find that Cuba, Pakistan, Egypt, Iran, Syria, the United States and Venezuela have held the summit hostage," Nicola Reindorp said.
"We wanted a bold agenda to tackle poverty but instead we have a brochure showcasing past commitments."
The BBC's diplomatic correspondent, Bridget Kendall, says the reforms now agreed upon are a far cry from what Mr Annan had been envisaging.
Mr Annan had warned that the UN faced a fork in the road and needed bold action to remain relevant.
Global literacy campaigners are among those lobbying the summit
About 150 presidents, prime ministers and monarchs are arriving at UN headquarters for the three-day summit.
It is being billed as the largest summit in the history of mankind and New York has mounted a massive security operation.
"This is a general assembly like no other," said New York Police Commissioner Ray Kelly who is deploying 4,000 officers for the event.
Secret Service teams will be protecting the foreign leaders and counter-terrorist units will be on hand while an 11km (seven mile) no-fly zone will be enforced.
Fashion Week coincides with the summit, and a "hell on wheels" is forecast for Manhattan's streets by the New York Post newspaper while local restaurants are expecting a bumper week.
Arriving along with the politicians will be Irish rock star Bob Geldof who helped organise the Live 8 anti-poverty concerts this summer.