* Geopolitical deadlock over next U.N. climate talks

* Russia blocking EU countries from hosting

* Ukraine war, geopolitics complicate decision

DUBAI, Dec 7 (Reuters) - Moldova has put itself forward as a candidate for the presidency of next year's U.N. climate summit and Serbia is also considering throwing its hat in the ring, according to people familiar with the matter and a document seen by Reuters.

The two countries' proposals are an attempt to resolve a geopolitical spat that has left the COP29 event without a host.

Talks on who will take over from current COP28 host the United Arab Emirates hit an unprecedented deadlock, with countries in the eastern Europe region, which is due to host the annual U.N. summit, unable to agree on a candidate.

Moldova has now volunteered to preside over the talks, according to a letter from the country to other Eastern European nations, seen by Reuters. The tiny land-locked country, however, has not volunteered to host the massive event, sources familiar with the matter said.

The sources told Reuters that Serbia was considering putting itself forward for both hosting and running COP29, but had yet to make a formal bid.

Whether either of these countries will win regional approval remains to be seen.

Under U.N. guidelines the president for a COP, short for Conference of Parties, rotates between five global regions and it is up to countries in that region to unanimously decide between themselves who takes it on.

Moldova's environment ministry and the office of Serbia's president did not respond to requests for comment.

Moldova and Serbia have each applied to join the EU. Moldovan President Maia Sandu has denounced Russia's invasion of Ukraine. Serbia is a traditional ally of Russia.

The COP president plays a key role in guiding talks among the nearly 200 countries present at annual U.N. climate talks, and usually one country takes on both the presidency and hosting of the summit.

If countries cannot approve a COP29 president, the UAE may have to keep the role for a second year. If countries cannot choose a new host, the summit's location could revert to Germany, where the U.N.'s climate secretariat is headquartered.

A spokesperson for the German foreign office said discussions were taking place among Eastern European countries to find a solution.

"Germany is aware that, as seat of the UNFCCC, it has a particular responsibility and role to play under the rules of the global climate conferences," the spokesperson added.

The geopolitical deadlock has left whichever nation ends up running COP29 with scarce time to prepare for the role, and some negotiators in Dubai said they expect next year's event to be a scaled-back affair, given the short time-frame.

"We have a very short time for any country that will be hosting... One year is not enough," Gayane Gabrielyan, Armenia's Deputy Environment Minister, told Reuters.

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(Reporting by Kate Abnett and Alexander Cornwell; additional reporting by Elizabeth Piper and Sarah McFarlane; editing by Miral Fahmy)