* Agreement keeps hopes for 2015 climate deal alive
* Warsaw talks go into overtime due to deadlock
* Delegates still discussing "climate aid"
By Alister Doyle and Nina Chestney
WARSAW, Nov 23 (Reuters) - Almost 200 nations kept a plan to reach a new U.N. climate pact in 2015 alive on Saturday when rich and poor countries reached a compromise on sharing out the efforts needed to slow global warming.
A two-week negotiation in Warsaw had been due to end on Friday, but was blocked over a timetable for the first U.N. climate accord that would set greenhouse gas emissions requirements for all nations. The pact is due to be agreed in 2015 and come into force after 2020.
Negotiators finally agreed that all countries should work to curb emissions - a process described in the jargon as "intended nationally determined contributions" - as soon as possible and ideally by the first quarter of 2015.
The agreement ended deadlock between rich and poor about sharing out the burden of limiting emissions blamed for causing more heatwaves, floods, droughts and rising sea levels.
Under the last climate pact, the Kyoto Protocol, only the most developed countries were required to limit their emissions - one of the main reasons the United States refused to accept it, saying rapidly growing economies like China and India must also take part.
"Just in the nick of time, the negotiators in Warsaw delivered enough to keep the process moving," said Jennifer Morgan of the World Resources Institute think-tank.
China had insisted that developing nations should announce deep cuts in emissions while allowing emerging economies room to burn more fossil fuels to help end poverty.
But the United States noted that all nations agreed in 2012 that the 2015 deal would be "applicable to all" and accused emerging nations of harping back to previous deals.
"I feel like I am going into a time warp. That is folly," said Todd Stern, the U.S. special envoy for climate change.
Developed nations had wanted all to take on "commitments", not the weaker-sounding "contributions" that they settled for.
Before Saturday, the only concrete measure to have emerged after two weeks was an agreement on new rules to protect tropical forests, which soak up carbon dioxide as they grow.
During the Warsaw meeting, no major nation offered tougher action to slow rising world greenhouse gas emissions and Japan backtracked from its carbon goals for 2020, after shuttering its nuclear industry after the Fukushima disaster.
Even after breaking the deadlock over which countries should tackle emissions, talks continued on another issue that has divided rich and poor: the aid that developed countries pay to developing ones to help them curb emissions and cope with to the impacts of climate change.
Developed nations, which promised in 2009 to raise aid to $100 billion a year after 2020 from $10 billion a year in 2010-12, have resisted calls to set targets for 2013-19.
A draft text merely urged developed nations, which have been more focused on spurring economic growth than on fixing climate change, to set "increasing levels" of aid.
The talks have also proposed a "Warsaw Mechanism" which would provide expertise, and possibly aid, to help developing nations cope with loss and damage from extreme events such as heatwaves, droughts and floods, and creeping threats such as rising sea levels and desertification.
Developing nations have insisted on a "mechanism" - to show it was separate from existing structures - even though rich countries say that it will not get new funds beyond the planned $100 billion a year from 2020. (Additional reporting by Susanna Twidale, Stian Reklev and Michael Szabo; Editing by Robin Pomeroy)