Bulgaria's ruling GERB party candidate, Rosen Plevneliev, is set to win a presidential election run-off on Sunday against Socialist Ivailo Kalfin with about 55 percent support, two exit polls showed.

Alpha Research and Gallup International polls put Plevneliev comfortably ahead of Kalfin who got 45 percent backing -- a victory which would strengthen Prime Minister Boiko Borisov's grip on power in the European Union's poorest state before 2013 general elections.

Plevneliev's winning the highly ceremonial presidential role, would remove the possibility of government-initiated legislation or appointments being vetoed by Socialist President Georgi Parvanov who has often criticised the cabinet.

GERB's victory means stable governance, said independent political analyst Rumiana Kolarova. It is definitely good for Bulgaria, because the cabinet will not be blocked.

Analysts also say Borisov is unlikely to risk potentially unpopular overhauls of areas such as healthcare and pensions but will keep tight fiscal discipline to protect the country's financial stability and will carry on with large-scale infrastructure improvement.

He will also be keen to demonstrate Bulgaria's progress by ensuring it joins the EU's passport-free Schengen zone, from which it has been blocked due to corruption concerns, before the 2013 election.

GRAFT FIGHT

The campaign was blighted by rallies against the Roma minority and corruption highlighting the cabinet's struggle to address unemployment, graft and the fragile position of ethnic minorities.

Former construction minister Plevneliev, 47, has pledged to step up efforts to fight corruption in the public sector and to work towards the approval of the bill authorising widespread confiscation of illegally obtained assets.

The cause in this election is very strong and important -- speeding up Bulgaria's development, Plevneliev said after casting his ballot, as quoted by GERB in a statement.

Previously manager of a major building company, Plevneliev has also announced plans to set up councils to monitor economic policy, as well as the much-needed structural reforms.

Plevneliev has a clear idea of what to do and how to do it, said teacher Yanka Georgieva, 49. He's a successful businessman, a successful politician and it's time to be a successful president.

Turnout was about 40 percent at 1500 GMT, organisers said, and official results from the second round in the presidential race and the local elections held on Sunday are expected on Monday.

Exit poll results showed GERB has also won the mayoral posts in the Black Sea city of Varna, the central city of Stara Zagora and the Danube town of Rousse among others.

(Additional reporting by Angel Krasimirov; Editing by Louise Ireland)