WARSAW (Reuters) - Building nuclear power plants is the cheapest way for Poland to curb carbon emissions in the coming decades, a government report said on Wednesday.

Poland, which generates nearly all its electricity from ageing, coal-fired power plants, is formulating a new national strategy aimed at modernizing its energy sector to make it more efficient and to cut carbon emissions.

The report said Eastern Europe's biggest economy would need to increase spending on power infrastructure to 26 billion-37 billion zlotys ($8.3-11.8 billion) annually from a current 18 billion in order to boost the efficiency of the sector.

The size of the investment will depend on the structure of the energy mix and the future costs of carbon emissions, according to the study issued by the government's analysts.

The report, which presents various scenarios for Poland's energy mix through to 2060, said having atomic energy in the mix represented the most cost-efficient future path.

"The cheapest way to reduce emission growth is the construction of nuclear power plants," it said.

Additional savings could be made by linking Poland's power network with neighboring countries, so that it could buy or sell electricity on a larger scale in future, it said.

A part of the government's energy strategy is to build a 3 gigawatt nuclear power plant initially expected to cost 50 billion zlotys and be completed by 2023 - but the project has already run into delays due in part to financing problems.

The plant would help Poland meet EU requirements to reduce carbon missions by diversifying to less polluting forms of electricity generation.

Warsaw is hosting this year's U.N climate talks on November 11-22.

(Reporting by Agnieszka Barteczko; Editing by Michael Kahn and Pravin Char)