GDANSK, Poland (Reuters) -- Poles voted in a presidential election on Sunday likely to confirm a sharp swing to the right and set a run-off between two men divided over how far to push free-market reforms and how much welfare the state can afford.

The last opinion polls gave moderate pro-business candidate Donald Tusk a slim lead over conservative Warsaw mayor Lech Kaczynski. Neither had enough support, however, to win outright and both were looking to a run-off in two weeks.

The presidential vote has complicated efforts by Tusk's and Kaczynski's parties to join in a coalition government after they trounced the ruling left in parliamentary elections last month.

The new coalition will have to deal with unemployment of 18 percent, the highest in the European Union, and impose economic reforms in the EU's largest new member state.

A Tusk or Kaczynski win would cement the swing to the right after four years of scandal-tainted leftist rule and two five-year terms for President Aleksander Kwasniewski, a former communist.

"I don't think I can win in the first round," Kaczynski told reporters after casting his vote.

Tusk, who voted in his home city of Gdansk, agreed.

"We will probably be voting in a second round and everything indicates that I will make it into the run-off," he said.

The polls predicted Tusk would win by a narrow margin in an October 23 run-off between the two former activists of the Solidarity movement that helped topple communism in 1989.

Polling stations opened at 6 a.m. (0400 GMT) and first exit polls were due after voting ends at 8 p.m. None of the remaining 10 candidates looks able to threaten the front-runners.

Balance of pwer
Whoever wins will have considerable powers. The president is commander in chief of Polish forces, has a say over foreign policy, can propose and veto legislation and nominate prime ministers and, in some circumstances, dissolve parliament.

Presidents have little direct influence over economic or social policy. But the election will determine the balance of power in the ruling coalition and the presidential race has prolonged uncertainty in financial markets about the scope and pace of reforms.

Mirroring a European Union-wide debate, the campaign between Tusk and Kaczynski centred on how quickly and how far to go with free-market reforms and how much welfare Poland can afford.

Tusk, 48, and his Civic Platform want to revitalise the economy by cutting red tape and taxes, saying this is the best way to put Poland's unemployed back to work.

The soft-spoken historian paints his party as a force for modernisation that can unite Poles, mend strained relations with big neighbours Germany and Russia and anchor the nation of 38 million in the European mainstream.

Kaczynski, 56, and his Law and Justice party promise a clear break from post-communist Poland under the banner of the "Fourth Republic", a return to Christian values while protecting workers' rights and the welfare state.

He promises a strong-willed Poland in the EU that does not seek closer integration and stresses a strategic partnership with the United States. Kaczynski said on Sunday that if elected he would first visit the Vatican and later Washington.

The conservatives have courted the religious right, shrugging off EU criticism over their calls to limit gay rights and support for death penalty.