By Yuri Kulikov and Sabina Zawadzki
KIEV (Reuters) - Ukrainians voted on Sunday for a new president in a run-off between Prime Minister Yulia Tymoshenko and opposition leader Viktor Yanukovich which could push the country into a fresh bout of instability.
Analysts expect a narrow victory for Yanukovich but Tymoshenko has threatened to call for protests if she deems the vote unfair, in a replay of the 2004 "Orange Revolution" that swept her and outgoing pro-Western President Viktor Yushchenko to power.
Any challenge to the poll result would further damage confidence in a country plagued by years of political bickering among the winners of the 2004 revolution, stalled policy-making and now, an economic crisis.
The euphoria of 2004, when protests overturned a rigged poll that gave Yanukovich victory, has disappeared and been replaced by a sense of frustration and fatigue.
"It would be terrible to vote for Tymoshenko. It would be shameful to vote for Yanukovich," said 27-year-old Natalya Zhuk. "Nothing in this country will change in the next five years."
Both Tymoshenko and Yanukovich hope to improve ties with Russia after relations with the ex-Soviet master deteriorated under Yushchenko. Both also hope for closer integration with the European Union, though Tymoshenko is seen as more enthusiastic.
But whoever wins will also have to make difficult spending cuts at home to bring back the International Monetary Fund and its unprecedented $16.4 billion bailout that was vital for the state coffers but suspended last year over broken promises.
Portrayed as a cheat and Moscow's stooge during the 2004 mass protests, Yanukovich is eying a remarkable comeback, adding to his support base those who are disappointed with the Orange leaders and suffering from the economic crisis.
"I am sure that the Ukrainian nation deserves a better life. That is why I have voted for good changes, for stability and for a strong Ukraine," Yanukovich said, smiling and looking relaxed, after casting his vote.
He led Tymoshenko by 10 percentage points in the first round on January 17. By 11 a.m. (9 a.m. British time) 17.6 percent of those eligible had voted. That is lower than in previous elections where over 20 percent voted, but slightly higher than the first round.
Reflecting the unhappiness of many, a group of semi-naked women calling themselves "Femen" overran the polling station where Yanukovich was due to vote with placards saying "Stop raping the country," asking people not to "sell" their votes.
Police said that voting, which ends at 8 p.m. (6 p.m. British time), was going smoothly in general. Exit polls are due shortly after.
The personal antagonism between the beefy, slow-speaking Yanukovich, 59, and the sharp-tongued Tymoshenko, 49, mirrors a gulf between the Russian-speaking east and nationalist west.
In the east and south, people have faith in Yanukovich's consistency, his ability to do business with Russia and see him as a strong man shaped by a rough childhood. He has served twice as prime minister -- the same as Tymoshenko.
"We lost five years of our lives thanks to Yushchenko and Tymoshenko," said Oleg Nochvyn, a miner in his 50s.
"For five years they were promising us -- tomorrow will be better. Well, I get up the next day and it's worse than the day before ... Under Viktor Fyodorovich (Yanukovich) we had everything -- economic growth, everything was getting better."
A tired Tymoshenko voted early in her native Dnipropetrovsk.
"I have just voted for a new Ukraine, a happy Ukraine, a rich, beautiful European state," she said. "I am sure only in such a state people will live happily, each person will find his place and I will serve this cause with all my soul and ability."
The former gas tycoon accused Yanukovich of preparing to cheat after his Regions Party pushed through parliament changes to voting rules, a charge Yanukovich throws back at Tymoshenko.
A spokesman of the Organisation for Security and Cooperation in Europe said the amendments should change little if voting officials work in good faith. The election arm of the OSCE will present its findings from its observations on Monday.
Yushchenko, Tymoshenko's former ally in the Orange Revolution but with whom she has since exchanged bitter recriminations, was eliminated in the first round of voting.
"I think Ukraine will be ashamed of its choice. But that is also democracy," the outgoing president said.
(Additional reporting by Natalya Zinets in Kiev and Lina Kushch in Donetsk; Writing by Sabina Zawadzki and Matt Robinson; editing by David Stamp)