Pared-down summit will force heads of rich states to listen to those of third world in hope of kickstarting radical action

The United Nations is planning a form of diplomatic shock therapy for world leaders this week in the hope of injecting badly needed urgency into negotiations for a climate change treaty that, it is now widely acknowledged, are dangerously adrift.

UN chief Ban Ki-Moon and negotiators say that unless they can convert world leaders into committed advocates of radical action, it will be very hard to reach a credible and enforceable agreement to avoid the most devastating consequences of climate change.

As the digital counter ticking off the hours to the Copenhagen summit – which had been supposed to seal the deal on climate change – hit 77 days today, progress at the UN summit in New York is seen as vital. Nearly 100 heads of state and government are to attend the summit, for which a pared-down format has been devised.

"We need these leaders to go outside their usual comfort zones," said one diplomat. "Our sense is that leaders have got a little too cosy and comfortable. They really have to hear from countries that are vulnerable and suffering."

Rajendra Pachauri, head of the Intergovernmental Panel on Climate Change, which won the Nobel peace prize with Al Gore, agreed. Commenting on the leaders attending the G20 summit in Pittsburgh next week, he said: "We need to remind these people about impacts of climate change – the fact that they are inequitable and fall very heavily on some of the poorest people in the world. We are likely to see a large number of failed states if we don't act in time."

The heads of state attending the UN summit are to be stripped of their entourages. Each will be allowed just one aide, generally their country's environment minister, in the sessions.

Instead of set-piece speeches, leaders will be paired off to chair discussion groups. Britain will be with Guyana, Tuvalu with the Netherlands, and Mongolia with the European commission.

The leaders will also lunch with environmental activists and chief executives of corporations who have been pressing their governments for action. At dinner, the leaders of the biggest polluting countries will dine with the leaders of Bangladesh, Kiribati and Costa Rica – which are among the primary victims of climate change.

By the end of the day, the rationale goes, the leaders will be imbued with a new sense of purpose. Leaders of rich countries will have been galvanised to take on the big emissions cuts – 25-40% over the next decade, 80% by 2050 – needed to keep temperatures from rising more than two degrees above pre-industrial levels, the temperature set by science to avoid the most calamitous effects of climate change.

The leaders will also, it is hoped, have some understanding of the threat to poorer countries. And, at the very least, they will have more of a common purpose in tackling the problem. "We need to gather together. We don't want to blame or point fingers at each other," said Yaqoub al-Sanada, counsellor at the Kuwaiti mission to the UN. Kuwait – one of the biggest producers of oil – will co-chair a discussion session with Finland.

The UN is hoping for help from Barack Obama. The US president will speak at the session, and there is anticipation he will deliver a strong signal that America is committed to action. There is growing anxiety for those kinds of reassurances, especially as opposition to Obama's green agenda grows in Congress. "The first question I get any time I meet with anybody is, 'Where's the legislation? How's it going?'," Todd Stern, the State Department's climate change envoy, said. There are also reports that China's president, Hu Jintao, in his first appearance at the UN, will announce new commitments to curb pollution – the kind of signal that will be crucial to boost negotiations in the days leading up to Copenhagen.

"We can get a successful outcome from Copenhagen. It is achievable, but at the moment it's in the balance," said John Ashton, Britain's climate change envoy. "We need to close the gaps."

Those gaps grew over the summer. There is what Ashton called the "ambition gap" – the failure of leaders of the big polluting countries to sign on to the deep emissions cuts needed. Then there is the "finance gap" – the failure of industrialised states to come up with a package on how to compensate poor countries that will suffer the most devastating consequences.

Britain came forward last June with an estimate of £61bn a year by 2020. Negotiators are frustrated that major industrialised states have not set clear figures on how much they are willing to commit, or how they will provide the funding.

Some climate change experts and negotiators have already begun planning a fallback position should the December Copenhagen summit fail to produce a strong enough agreement.

In Washington, Obama administration officials now talk openly about negotiating beyond Copenhagen. "Let's not make that one particular time the be-all and end-all, and say that if it doesn't happen we are doomed," Steven Chu, the energy secretary, told reporters.

Thinktanks are already starting to work on what is being called "Plan B" – scenarios for how the world could come up with an action plan before it is too late. But some are not holding their breath.

"It seems to me that Copenhagen is not the end of this," said Tim Wirth, the president of the UN Foundation, and the man who, in the 1980s, helped to write the first cap-and-trade plan for acid rain. He added: "We are going to have Copenhagens for the rest of our lives."