By Ben Garside and Valerie Volcovici

LONDON/WASHINGTON (Reuters) - United Nations Secretary General Ban Ki-moon this month hopes to reinvigorate the years-long effort to forge a global climate deal, even as concerns grow over whether the final pact will be rigorous enough to address threats to the environment.

Ban wants heads of state at a Sept. 23 gathering in New York to outline how their countries will contribute to a mutual goal to contain rising temperatures, said Selwin Hart, the Barbadian diplomat helping to spearhead the conference. The final deal is due to be signed in Paris in 2015.

Hart said the event will avoid some of the thornier questions surrounding the ultimate outcome of the Paris summit, but should give a good indication of how serious countries are.

“What we are looking for is countries to signal a commitment to a universal and meaningful global deal, and signal their ambition,” Hart told Reuters.

The summit will feature “unprecedented” participation of non-government organizations and the private sector, Hart said. Several hundred leaders from major banks, the oil and gas industry, and the agricultural sector will attend and are expected to make major “financial contributions."

These contributions will center around eight key action areas identified by Ban. They include cities, energy, transportation and climate resilience.

President Barack Obama is expected to be among the 100 or so heads of state at the summit, but observers worry that the goal of securing a global deal in 2015 could be in peril if certain other high profile leaders decide to skip the meeting.

Tony de Brum, foreign minister for the Marshall Islands, one of several low-lying South Pacific nations vulnerable to rising sea levels, was alarmed by recent reports that China’s President Xi Jinping and India’s Prime Minister Narendra Modi were not planning to attend.

“We expect solidarity from our developing country compatriots, not excuses,” de Brum said.

A few countries may be ready to declare the methods they intend to employ to curb greenhouse gas emissions post-2020, well ahead of a March 2015 deadline to submit these plans to the U.N. Framework Convention on Climate Change (UNFCCC).

Taking part in a similar summit in 2009 were nearly 100 heads of state, including Hu Jintao, the first Chinese president in 40 years to go to New York to address the U.N. General Assembly.

But months later, leaders at the Copenhagen U.N. climate summit failed to finalize a binding deal on emissions curbs, although they did agree on a goal to prevent temperatures from rising more than 2°C above pre-industrial levels.

The Copenhagen Accord began to move countries away from negotiating a legally-binding treaty like the 1997 Kyoto Protocol, never ratified by the United States, toward a system of voluntary pledges meant to bring major emerging economies on board with measures to protect the environment.

Yvo de Boer, UN climate chief during the Copenhagen talks, said Ban’s latest summit should have an energizing effect, but after 20 years of contentious negotiations, drastic changes are not expected.

"If nothing's happening in the climate process, it’s because the leaders are not providing the mandates (to the negotiators)... and that's because they are not understanding the issues and haven't talked to each other enough about how to advance," de Boer said.

Some observers question whether declarations made in New York will even translate into a future agreement that keeps countries on track to achieve the 2-degree goal.

Jonathan Grant, a consultant at global advisory firm PwC, said based on the types of national contributions some countries are expected to make, the world is headed to a more damaging 3 degree temperature rise.


(Reporting by Ben Garside in London and Valerie Volcovici in Washington, editing by Ros Krasny and Gunna Dickson)