* Civic Platform led Law and Justice in opinion polls
* Civic Platform says it guarantees stability, reform
* Law and Justice victory could test Russia, Germany ties (Adds turnout figures, president and ex-president)
By Gabriela Baczynska and Rob Strybel
WARSAW, Oct 9 (Reuters) - Poland voted in a parliamentary election on Sunday that could give Prime Minister Donald Tusk's centre-right Civic Platform four more years in power to pursue gradual economic reforms and preserve political stability.
Civic Platform, which guided Poland through the 2008-2009 financial crisis and favours closer ties with the rest of the European Union, would be the first party to hold on to power in an election in Poland since Communism collapsed in 1989.
Tusk, 54, has promised to continue cautious economic reforms if he retains power, and has made clear he will press on with efforts to ensure stable relations with Poland's large and powerful neighbours, Germany and Russia.
But some opinion polls before the election showed former premier Jaroslaw Kaczynski's conservative-nationalist Law and Justice party catching up in second place, and pollsters said it could challenge Civic Platform if the voter turnout is low.
The election commission said 23 percent of voters had cast ballots by 2.00 p.m. (1200 GMT) and commentators said this could point to a low turnout.
Kaczynski rails against Germany and Russia and his return to power after four years in opposition could threaten ties with Poland's largest neighbours, and political stability, but he would have difficulty building a stable coalition.
"Democracy is strong through participation. With a 20-30 percent turnout, democracy wilts before our very eyes. I hope the turnout will be at least middling and not dramatically lower than normal," former president Aleksander Kwasniewski said.
No party is expected to win an outright majority and another four years of coalition government are likely in the country of more than 38 million people after Civic Platform's four-year alliance with the Peasants' Party.
President Bronislaw Komorowski, who hails from Tusk's party, made clear he expected coalition talks to start quickly after the election and added: "I will begin them with the leader of the victorious party."
FATE OF REFORMS
Tusk portrays himself as a guardian of stability. A mild-mannered pragmatist with a common touch, he has eschewed radical economic reforms, avoided talk of austerity despite a large budget deficit and promised to continue cautious reforms.
"PO (Civic Platform) should continue to govern because they have done a great deal. Just look at the roads," said Maria Mlodzikowska, an 80-year-old retired physical education teacher, after voting in Warsaw.
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 privatisation. The Law and Justice-led coalition collapsed in acrimony in 2007.
Jan Mazur, a 74-year-old retired printer, said he had voted for Law and Justice for the sake of his grandchildren.
"I don't want them to grow up in a country which owns nothing because the PO has sold everything off under the pretext of what they call privatisation," he said.
Ratings agencies say 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. The current coalition, however, has failed to deliver on promises of far-reaching liberal market reforms.
The EU's largest former communist economy has lost some of its lustre since 2007, but Poland was the only EU state to maintain positive growth through the turmoil of 2008-2009 and growth is forecast to be about 4 percent this year.
FOREIGN POLICY CHALLENGES
If Tusk wins but cannot build a strong coalition with just the Peasants' Party, he could turn for support to leftist deputies or parties, or to Palikot's Movement, a new party that has criticised the powerful Catholic Church.
The party, led by Civic Platform defector Janusz Palikot, supports gay rights, abortion and legalisation of soft drugs.
"I support Palikot ... at least he'll be a breath of fresh air in the stiflingly stodgy Sejm," said Krystyna Celinska, a 28-year-old graphic artist.
Tusk favours deeper EU integration for the NATO member state and has built up relations with Moscow and Berlin.
Kaczynski, 62, distrusts both -- Poland was carved up under a Nazi-Soviet pact before World War Two -- and raised eyebrows during the election campaign by repeating in a new book his view that Berlin is trying to subdue Poland.
"I back PiS (Law and Justice) because they put Poland's interests ahead of those of Brussels or Berlin," said Maria Derkacz, a translator in her early 60s.
Tusk has continued the rapprochement with Moscow, which held sway over Poland for decades after World War Two, despite strains over a plane crash last year that killed then-President Lech Kaczynski, Jaroslaw Kaczynski's twin, and 95 others. (Additional reporting by Rob Strybel; Writing by Gabriela Baczynska and Timothy Heritage; Editing by Maria Golovnina)