* Main opposition narrowing gap with PM Tusk's centrists
* Analysts see lower turnout helping Kaczynski in Oct.9 race
* Small gap means difficult coalition-building after vote
By Gabriela Baczynska and Pawel Sobczak
WARSAW, Sept 26 (Reuters) - Poland's election is shaping up to be much tighter than expected, increasing the risk Prime Minister Donald Tusk may struggle to build a stable coalition after the Oct. 9 vote.
Tusk's centrist Civic Platform (PO) continues to lead in opinion polls but the main opposition party, the conservative Law and Justice (PiS), is narrowing the gap.
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* PiS is enjoying a strong election campaign, analysts say with their call for more public spending than PO at this time of crisis. Latest opinion polls show the gap with PO down to some 5-9 percentage points from a previous range of 12 to 18 points.
The latest survey gave PO a lead of 5 percentage points on Sunday .
No poll has yet shown the two main rivals at level pegging or PiS pulling ahead.
PiS leader Jaroslaw Kaczynski, who served as prime minister in 2006-07, will continue touring Poland during the two final weeks of the campaign, believing face-to-face meetings with people in smaller towns will provide a last-minute boost.
* PiS caucus leader Adam Lipinski said over the weekend the party's own surveys now suggested the race was so tight that either party could emerge with a lead of just 2-3 points.
"In such a case, we would likely seek the support of a smaller parliamentary faction, most likely the PSL, (Peasants' Party) to create a government," Lipinski told Reuters.
PSL is the current junior coalition partner of PO and Tusk has said he wants the duet to continue after the election. Unlike many other parties, PSL has not ruled out a future coalition with PiS.
* A senior PO member told Reuters the most likely outcome was that his party would lead with 6-8 points.
That would put the result close to last year's presidential race in which PO's candidate, Bronislaw Komorowski, though widely seen as a likely clear winner, in the end came just 6 points ahead of Kaczynski in an election sparked by a plane crash in which Lech Kaczynski, the PiS leader's twin brother, died along with 95 others.
Analysts and media had speculated the personal tragedy might even lead Kaczynski to withdraw from politics but he sees his continued political involvement as a moral duty to the memory of his late brother.
* Many analysts expect a lower turnout this year, possibly closer to 40 rather than 50 percent, which in the past has helped PiS, whose core electorate -- often elderly, rural and Catholic -- is more disciplined about voting than the younger urban voters who in the past helped PO win.
President Komorowski, a long-time Tusk ally, has issued an appeal to all Poles to go out and vote on Oct 9.
"Turnout in Poland is traditionally between 40 and 55 percent and it will be within this band most likely this time as well, largely depending on what opinion polls will be showing in the last two weeks of campaigning," said Radoslaw Markowski of the Polish Academy of Sciences.
"If surveys show a narrow gap between the two, turnout will be higher. If they show PO winning easily, it'll be lower."
* PO has disappointed some younger voters by not delivering on far-reaching liberal market reforms, while its more traditionalist, Catholic wing blocked plans to introduce state subsidies for in vitro fertilisation (IVF) or grant more rights to same-sex couples.
Some young people now say they would abstain from voting or else back smaller parties like the libertarian, anti-clerical party of Janusz Palikot, a former PO lawmaker, who wants to legalise marijuana and abortion, widen gay rights and end compulsory religious education in schools.
It would come as a great surprise if Palikot's Support Movement (RPP) party cleared the five-percent threshold set to win seats in the Polish parliament, but at least two surveys recently signalled that may happen.
* Some analysts say, however, the recent strengthening of support for PiS may also help PO mobilise its voters, many of whom fear the return of Kaczynski to power.
They remember his clashes as prime minister with state prosecutors, the media, academics and the medical profession and also the increased tensions with the European Union, Germany and Russia. (Writing by Gabriela Baczynska, editing by Gareth Jones and Matthew Jones)