By Pavel Polityuk and Richard Balmforth
KIEV (Reuters) - Ukrainian President Viktor Yanukovich's party looks set to win a parliamentary majority after Sunday's election, but it may be hard pressed by an opposition boosted by resurgent nationalists and a liberal party headed by boxing champion Vitaly Klitschko.
Leaders of the ruling Party of the Regions claimed victory after exit polls put it in the lead with 28-30 percent of the voting in the part of balloting conducted by party lists.
A senior Regions official said he expected the party to pick up two thirds of the remaining vote in individual districts, ensuring it of a simple majority in the 450-seat assembly. There were no immediate reliable figures to provide a possible breakdown of seats.
But the shock of the night came from the Ukrainian nationalist Svoboda (Freedom) party which exit polls said took about 12 percent of the party list voting, assuring it of representation in parliament for the first time.
The strong showing by Svoboda - which is based in the Ukrainian-speaking west and occupies the opposite end of the political spectrum to the Regions - boosted opposition ranks, weakened by the jailing of Yanukovich's rival, Yulia Tymoshenko.
The other new wild card in the forthcoming parliament was that of Klitschko's UDAR (Punch) party which was in third place behind the Regions and the united opposition which includes Tymoshenko's Batkivschyna (Fatherland), according to the exit polls.
Victory by the Regions is certain to cement the leadership of Yanukovich, who comes up for re-election in 2015 and whose rule has been marked by an accumulation of presidential powers and antagonism with the West over Tymoshenko's imprisonment.
Tymoshenko, the country's most vibrant opposition figure, was jailed for seven years last year for abuse of office relating to a 2009 gas deal with Russia which she made when she was prime minister. The Yanukovich government says the agreement saddled Ukraine with an enormous price for gas supplies.
The former Soviet republic of 46 million, a major exporter of steel and grain, is more isolated politically on the international stage than it has been for years. Apart from being at odds with the United States and the European Union over Tymoshenko, Ukraine does not see eye to eye with Russia which has turned a deaf ear to Kiev's calls for cheaper gas.
At home, the government is also blamed for failing to stamp out corruption and has backed off from painful reforms that could secure much-needed IMF lending to shore up its export-driven economy.
Though these three opposition parties appeared to have won roughly half of the vote on party lists, they were not expected to fare as well in the single-mandate constituencies, results of which will only begin to emerge on Monday.
Borys Kolesnikov, a deputy prime minister, said he foresaw the Regions picking up two thirds of these individual districts.
"The exit poll data speaks for itself. It is clear the Party of the Regions has won ... These elections signal confidence in the President's policies," Prime Minister Mykola Azarov told journalists.
With the West seeing the poll as a test of Ukraine's commitment to democracy after Tymoshenko's imprisonment, interest will focus on the judgment which observers from the OSCE European security and human rights body will hand down on Monday.
Arseny Yatsenyuk, head of the united opposition in the absence of Tymoshenko, said: "The exit poll results have shown that the people of Ukraine support the opposition and not the government."
If the exit polls are proven accurate, Klitschko, the WBC heavyweight boxing champion, will now enter parliament at the head of his new party after a campaign in which he has been critical of corruption and cronyism under Yanukovich's rule.
He says his party will team up with Yatsenyuk and other members of the opposition, including Svoboda, though his refusal to join a pre-election coalition engendered suspicion.
"We do not foresee any joint work with the Party of the Regions and its communist satellite. We are ready to work with those political parties which propose a European path of development," Klitschko told journalists.
But it was the showing of Svoboda, which pursues a strong Ukrainian nationalist agenda and opposes attempts by the Regions to promote the Russian language over Ukrainian, which caught attention on the night.
Svoboda leader Oleh Tyahnybok, a 43-year-old surgeon, pledged to stick by a pre-election agreement and work with Yatsenyuk and other opposition leaders in the new parliament.
He appealed to Klitschko to formally join the united opposition. "We can only hope that, having looked at the situation which has emerged, Vitaly Klitschko will unite with us," he said in televised comments.
"Svoboda is the biggest sensation," said political analyst Volodymyr Fesenko of the Penta think tank. "The Ukrainian political borsch (soup) has got a bit more spicy. There will be more pepper but how it is going to taste is another question," he said.
Fesenko added that he saw the vote for Svoboda as reflecting a protest against the political establishment.
(Writing By Richard Balmforth; editing by Christopher Wilson)