Prime Minister Donald Tusk's candidate won Poland's presidential poll but the narrowness of the victory cast doubt on the government's ability to carry out unpopular reforms ahead of a 2011 parliamentary election.

Bronislaw Komorowski, a moderate conservative from Tusk's Civic Platform party (PO), won 53.0  per cent of votes in Sunday's poll, final official results showed, after a cliff-hanger vote that saw his right-wing rival Jaroslaw Kaczynski perform much better than expected.

Turnout was 55.3  per cent, higher than in a first round on June 20, despite the start of the summer vacation period.

Political analysts said the unexpected closeness of the presidential race, the prospect of looming local elections and the parliamentary vote next year could lead Tusk to take a cautious approach to introducing painful economic reforms.

Komorowski's win was "market positive", Goldman Sachs said in a note to clients. "However, these reforms look increasingly unlikely to happen quickly as local and parliamentary elections are approaching."

In Poland, the government sets policies, but the president can propose and veto laws, has a say on foreign policy issues and appoints key state officials.

The ruling Civic Platform faces an elevated budget deficit, high public debt, a public health system in disarray and an inefficient pension system. Changes in the pension system could hit farmers, miners and teachers, among others.

Kaczynski, who heads the main right-wing opposition party and was vying to succeed his twin brother Lech whose death in a plane crash in April precipitated the vote, scored 47  per cent, final results announced by the election commission showed.

Lech Kaczynski vetoed some of Tusk's reforms in the past.

Cabinet reshuffle possible

Newspapers urged the PO to deliver on promised reforms, with the Gazeta Wyborcza daily saying Tusk would lose next year's parliamentary election if he failed to do so.

Russia's President Dmitry Medvedev became one of the first foreign leaders to welcome Komorowski's victory. Moscow and Warsaw have been trying to repair long-strained ties, especially since Lech Kaczynski's death in the plane crash in Russia.

U.S. President Barack Obama also called Komorowski to congratulate him and invite him to visit Washington, the White House said. Poland and the United States signed an agreement on Saturday to allow the two nations to station U.S. missile interceptors on Polish soil, despite Russian objections.

Financial markets also cheered Komorowski's win and the Polish zloty firmed slightly against the euro and the dollar.

On Sunday night, Tusk vowed to push ahead with his plans to introduce an anchor on public spending. His finance minister, Jacek Rostowski, said a cautious 2011 budget was now crucial.

The European Union's largest ex-communist member was the only economy in the 27-nation bloc to avoid recession last year, but a sharp slowdown has hammered tax revenues and driven up the budget deficit to 7  per cent of gross domestic product (GDP).

Public debt, though low by west European standards, is creeping towards the 55  per cent of GDP threshold which, if breached, would by law trigger painful spending cuts.

Hurdles

Despite overcoming the risk of a presidential veto, PO faces other hurdles in the way of reforms. It is locked in a coalition with the small Peasants' Party which is opposed to any attack on the pension privileges of farmers and other groups.

Economy Minister Waldemar Pawlak, who heads the smaller coalition party and lost in the first round of the election, said the government should take the opportunity to first tackle bureaucracy that is stifling growth.

"It's important for the economy to remove administrative costs that are a burden for corporations," he said.

Komorowski, a gently-spoken father of five grown-up children, will be Poland's fourth democratically elected president since the fall of communism in 1989.

Conceding defeat on Sunday, Kaczynski told supporters his good result in the election also boded well for local elections in the autumn and next year's parliamentary poll, which Poland will hold during its rotating European Union presidency.

"We have to win them and we will," Kaczynski said. – Reuters