Poles are voting in a parliamentary election Sunday, likely to give the ruling center-right Civic Platform four more years in power to press on with gradual economic reforms and closer ties with the European Union.

Prime Minister Donald Tusk's Civic Platform led the final opinion polls, but outspoken former premier Jaroslaw Kaczynski's conservative-nationalist Law and Justice party narrowed the gap in some polls at the end of campaigning.

No party is expected to be able to rule alone, and Tusk is likely to turn to his current coalition partners, the Peasants' Party, if he wins. But opinion polls show Palikot's Movement, a new party that supports gay rights, abortion, and legalization of soft drugs, could emerge as a potential partner.

Tusk, who steered the country of more than 38 million people safely through the 2008-09 global financial crisis, has portrayed himself as a guardian of stability and said he will continue his cautious approach to economic reforms if he wins.

Law and Justice has promised more state involvement in the economy, including a bank tax and higher taxes for the rich, and vowed to wind down large-scale privatization carried out since Civic Platform took power in late 2007.

For me the choice really is about living standards, especially for the poor, Wanda Kalisz said, while having a cigarette outside a polling station in downtown Warsaw, shortly before it opened.

I'm close to retirement, and I just hope somebody would take care of me. So Kaczynski is a better choice, though for the younger and wealthier, maybe it's Tusk, she added.

Even if Law and Justice wins the most votes, it would be likely to struggle to put together a coalition.

More than 30 million people are eligible to vote. They will elect 460 lawmakers in the lower house, the Sejm, and 100 to the upper chamber, the Senate.

Voting started at 7 a.m. (0500 GMT) and ends at 9 p.m. (1900 GMT), when the first exit polls will be released. The official result will take several hours to come in.

Economic Challenges

Poland's main immediate challenge is to curb the public debt and deficit, which ballooned during the financial crisis.

Ratings agencies have said they could downgrade Poland if it does not swiftly act to reduce the budget deficit, expected to reach 5.6 percent of gross domestic product this year, and the public debt, expected to reach 53.8 percent of GDP this year.

Economists doubt Law and Justice would be able to meet the challenge and a short-term sell-off would be likely on Polish financial markets if it won.

However, the current coalition has failed to deliver on the far-reaching liberal market reforms Tusk originally vowed.

Civic Platform is likely to woo the Peasants' Party again, and Tusk has said he would not want to rule in a tri-party coalition. Sources in his party have said it might try to win over individual leftist lawmakers if it is close to a majority.

But the new libertarian party led by Janusz Palikot, a wealthy businessman and former Civic Platform lawmaker, has emerged as a potential partner after a late surge in opinion polls. It has criticized Poland's powerful Catholic Church.

The outcome could depend heavily on how many people vote as a low turnout is likely to favor Law and Justice, whose core electorate is traditionally loyal.

Any prolonged uncertainty over the shape of the coalition could unsettle financial markets in Poland, which holds the EU presidency until the end of this year, a largely formal role.

Foreign-Policy Agenda

At stake also is Poland's international agenda. Tusk, who is strongly pro-EU despite the Eurozone debt crisis, differs on foreign policy with Kaczynski, who deeply distrusts Poland's largest neighbors, Germany and Russia.

Tusk made improving ties with Germany, which occupied Poland during World War Two, a priority after relations sank under Poland's previous government, led by Kaczynski. Kaczynski raised eyebrows in Germany again this week by repeating in a new book his view that Berlin is trying to subdue Poland.

Tusk also has embarked on a cautious rapprochement with Moscow, which held sway in Poland for decades until the collapse of communist rule in Poland in 1989.

However, this policy suffered following a plane crash in Smolensk in western Russia that killed then-President Lech Kaczynski, Jaroslaw Kaczynski's twin, and all 95 others on board

Moscow says mistakes by Polish pilots were the sole cause of the crash in April 2010. Warsaw says it believes Russian ground controllers also played a role in the tragedy.

Kaczynski accuses Tusk of betraying Poland's national interest in Warsaw's dealings both with Berlin and Moscow, and he believes Tusk and Russian Prime Minister Vladimir Putin bore some responsibility for his brother's death.

Kaczynski's combative rhetoric on that issue has enabled Civic Platform to highlight the risks it says would stem from any return to power of Law and Justice by deepening social divisions and antagonizing Poland's allies.

(Writing by Gabriela Baczynska; Editing by Michael Roddy)