Ukraine needs energy plan for Russia ties-US official

* Ukraine needs "tough" energy decisions - U.S. official

* Moscow-Kiev relationship seen totally changing

KIEV, July 21 - Ukraine could change its entire relationship with Russia if it takes tough decisions on energy that would make it less dependent on gas from its former Soviet master, a senior U.S. administration official said on Tuesday.

"If Ukrainians were able to get to the level of Poland in terms of energy efficiency then they would be able to significantly cut their needs for gas imports," said the official, speaking on condition of anonymity.

Ties between the ex-Soviet neighbours sank after Ukraine's 2004 "Orange Revolution". Kiev has sought closer integration with the West and has accused Russia of exerting power over the region through its grip on the energy sector.

"If that (reduce gas imports) were to happen, then that would significantly change Ukraine's relationship with Russia," the official said.

Ukraine has had repeated rows with Russia over increasingly expensive gas prices and the latest disputes led to supply cuts to millions of Europeans in winter earlier this year.

The European Union, Russia and international financial organisations are in talks with Ukraine to provide what the official described as "significant investments" to help upgrade its gas transit system and pay for storage gas in advance.

The EU gets a fifth of its gas needs from Russia via Ukraine and in wintertime Ukraine must store extra gas to ensure smooth transit towards the bloc.

But in return the EU wants Ukraine to modernise and make transparent its energy sector and to increase prices for Ukrainians to ensure the viability of state energy firm Naftogaz, frequently at the centre of spats with Russia.

"If all this goes forward, the entire nature of the energy system will change here (in Ukraine)," the official said.