By Tsvetelia Tsolova
SOFIA (Reuters) - Ruling party candidate Tsetska Tsacheva is likely to narrowly win Bulgaria's presidential election on Sunday but could lose a subsequent runoff to Socialist contender Rumen Radev, polls suggest, heralding a shift towards closer ties with Russia.
On Friday, pollster Alpha Research showed Tsacheva, 58, a senior member of the GERB party, at 26.3 percent support, less than four percentage points over Radev, 53, a former air force commander.
But Gallup International pollsters said late on Thursday she would lose a Nov. 13 runoff vote, to be held if no candidate wins an overall majority on Sunday, by 47 percent to Radev's 53 percent. That outcome was similar to forecasts by Market Links and Mediana polls earlier this week.
Radev has pledged to cultivate better relations with European Union member Bulgaria's historical ally, Russia, and a removal of EU sanctions imposed on Moscow over its role in the separatist conflict in eastern Ukraine. The sanctions regime has caused some damage to Bulgaria's economy.
Although the job of president is largely ceremonial in Bulgaria, his victory could embolden opposition groups to seek to unseat Prime Minister Boiko Borisov's GERB minority government, possibly triggering early elections.
"If GERB loses this election, early general polls are very likely," said Kiril Avramov, political analyst with New Bulgarian University.
GERB remains the most popular political faction but public dissatisfaction over the pace of health and education reforms and Borisov's anti-corruption efforts have eroded its support.
Public backing for Tsacheva has eroded from 29.3 percent seen at the start of the campaign last month, while Radev's popularity rose to 22.5 percent from 21.4 percent, an Alpha Research poll conducted between Oct. 30 and Nov. 2 indicated.
Gallup's survey carried out between Oct. 24-30 put support for Tsacheva at 27.2 percent and 23.1 percent for Radev in the first round.
With 19 other candidates vying for Bulgaria's top office, the outcome of the Nov. 13 run-off is wholly up in the air, according to pollsters.
Bulgaria, a Black Sea state dependent on Russian energy supplies and popular with Russian tourists, shook off communist rule under Soviet domination a quarter of a century ago, but loyalties remain divided between Moscow and Brussels.
Radev has said Sofia needs to lead a foreign policy based on the country's national interest and that included improving links with Russia. "We lost a lot by more or less declaring Russia our enemy," he said on national Darik radio last month.
(Reporting by Tsvetelia Tsolova; editing by Justyna Pawlak and Mark Heinrich)