* Agenda for work on new global climate deal is adopted
* Agreement breaks week-long deadlock over procedure
* Mistrust between countries remains
* Urgent climate action needed to limit global warming (Adds further context, quotes)
By Nina Chestney
BONN, May 25 (Reuters) - More than 180 countries agreed on an agenda for work on a new climate treaty by 2015 at United Nations climate talks on Friday, breaking a deadlock over procedure, but mistrust remains that could threaten progress for the rest of the year.
"(The workplan) was not an easy issue to agree (on)," U.N. climate chief Christiana Figueres told reporters after the negotiations held at Bonn in Germany.
"All parties needed reassurances from each other to allow them to undertake the work with a certain sense of comfort."
U.N. climate talks in South Africa last year agreed a package of measures that would extend the 1997 Kyoto Protocol after it expires at the end of this year and decide a new, legally binding accord to cut global greenhouse gas emissions by 2015, coming into force by 2020.
In the Bonn talks, the first negotiation session since that deal was struck, delegates have argued for over a week on how to organise work on a new climate deal and appoint a chair to steer the process.
Procedural wrangling during the two-week session, attended by national negotiating teams below ministerial level, has shown there is mistrust among participants and heaps pressure on ministerial talks in Doha, Qatar, at the end of the year to deliver, observers said.
"When people start fighting about agendas it is a symptom of lack of trust and of some pretty substantive areas of disagreement," said Celine Charveriat, director of advocacy and campaigns at international development charity Oxfam.
The European Union and others have accused China, along with other developing countries, of "procedural blocking" or trying to backtrack on the Durban deal by altering the approach to negotiations.
One initiative, an attempt to bring discussion on emissions cuts by both rich and poor countries into one forum, rather than keep it in two separate negotiating tracks, is no longer an obstacle to progress but others may emerge.
"We cleared a difficult hurdle here. There is no doubt that it will be the first of many, and we must remember that time is not on our side," said Sai Navoti, lead negotiator for the Alliance of Small Island States, which represents small nations most vulnerable to global warming.
On the other side, developing countries accuse the United States, the EU and other rich nations of trying to avoid making deeper emissions cuts and dodging increases in finance to help poorer nations deal with climate change.
Environmentalist groups and countries that are particularly vulnerable to the effects of climate change warn time is running out to avert disastrous consequences like increased extreme weather, ocean acidification and glacier melts.
Meanwhile a lot of work remains for this year, including agreeing on the length of an extension of the Kyoto Protocol, which nations will sign up to it and their level of emissions cut ambitions, as well as the means to raise $100 billion a year of finance by 2020 to help developing countries tackle climate change.
Countries have agreed that deep emissions cuts are needed to limit a rise in global average temperature to less than 2 degrees Celsius this century above pre-industrial levels, a threshold that scientists say is the minimum required to avert catastrophic effects.
However, one of the main contributors to global warming, global carbon dioxide emissions, hit a record high last year, according to the International Energy Agency, which advises industrialised countries.
Some countries also look set to miss their emissions cut targets for 2020, putting the world on a dangerous trajectory towards a rise in global average temperature of 3.5 degree Celsius, research showed on Thursday.
"The majority of countries want to move forwards faster but..a relatively small group is holding up what the rest of the room wants," said the European Union's chief negotiator Artur Runge-Metzger.
Only six months remain before the Doha meeting. Some nations want extra negotiating sessions before then but between 4.4 million euros and 4.8 million euros of funding will have to be pledged by countries by Monday to guarantee that, Figueres said.
Some small steps forward were made at the talks.
"The positive thing is there is discussion around more ambitious emissions cuts (to 2020) but that needs to be translated into action. At least no country thinks it can evade the issue," said Oxfam's Charveriat.
"Countries are still under pressure to continue substantive deliberation to allow them to go to Doha with a draft (negotiating) text," Figueres added. (Editing by Anthony Barker)