By Tsvetelia Tsolova and Sam Cage
SOFIA (Reuters) - The rightist GERB party held the lead in Bulgaria's election on Sunday but its prospects of forming another government, after the last one was ousted by protests, looked uncertain after its potential partner ruled out a deal.
Turnout was the lowest in post-communist history, at around 53 percent, reflecting the disaffection with the political elite in a country where unemployment is close to an eight-year high.
GERB, which resigned in February after often violent demonstrations against poverty and corruption, was set to win 31 percent of the votes, ahead of the Socialists on 25-27 percent, exit polls by Alpha Research and Sova Harris agencies showed.
Deputy leader Tsvetan Tsvetanov said GERB could consider a minority government with backing from others, but its most likely partner, the nationalist Attack, ruled out support for a GERB-led government to lead the country of 7.3 million.
"GERB will be responsible to the nation," a subdued Tsvetanov told national television, adopting a conciliatory rather than triumphant tone. "Our leader is capable of proposing and forming a government - it could be a minority one."
A delay in forming a new administration may raise questions over economic policy, with low debt needed to maintain confidence in a currency pegged to the euro, and hinder growth. It may ultimately mean a new election.
All parties had waged a low-profile campaign, with few political posters in Bulgaria's towns and villages, where half-finished buildings evoke memories of the credit boom and bust under the 2005-2009 Socialist-led government.
They also dropped their usual post-election rallies.
About 200 people gathered in Sofia as polls closed, waving Bulgarian flags and banners criticizing GERB and the political elite, briefly scuffling with police.
But the protests were nothing like those earlier this year when thousands took to the streets and seven people set themselves on fire in disgust at corruption and organized crime and at how one in four Bulgarians still live below the poverty line, six years after joining the European Union.
Pollster Alpha Research predicted GERB would win 97 of the 240 seats in parliament and the Socialists 85, leaving both needing partners to form a majority coalition - likely to be fragile given the bad feeling after an ill-tempered campaign.
Two other parties - the ethnic Turkish MRF, a previous partner of the Socialists, on 10-11 percent, and Attack on 7-8 percent - were set to enter parliament.
Attack leader Volen Siderov said his party could not support GERB - although analysts said this might be a negotiating position and a deal could still be possible.
"We cannot support someone who has declared anti-state and anti-Bulgarian policies," Siderov told reporters.
A new pro-business party, Bulgaria for the Citizens, could also beat the 4 percent threshold, which would reduce other groups' seats. First official results are expected on Monday.
GERB pledges to keep debt down and maintain economic stability, winning favor from investors, and supporters praise it for building schools and motorways. The Socialists say they will spend more, creating jobs and lifting growth above the 1 percent expected this year.
Under GERB, led by former bodyguard Boiko Borisov, Bulgaria has kept one of the lowest debt levels in the EU but its opponents say that has constrained growth in the country where the average monthly wage is 400 euros ($520).
About 2 million Bulgarians have left since the 1989 fall of communism and the country still struggles to supply running water and reliable electricity to some of its people.
GERB's campaign was marred by allegations of illegal wiretapping and the seizure of illegal ballot papers at a printing shop owned by one of its local councilors, increasing fears of vote rigging although there have so far been no significant complaints.
"The law protects politicians and they protect criminals. They are connected while we are still the poorest country in the European Union," IT specialist Kalin Borislavov, 28, said in Sofia.
(Additional reporting by Angel Krasimirov; Editing by Alison Williams)