By Katarzyna Pieniadz and Adam Jasser

WARSAW, Aug 8 (Reuters) Polish political parties are preparing for early elections, perhaps this autumn, because of the growing likelihood that Prime Minister Jaroslaw Kaczynski will be unable to hold together his coalition government.

Officials from Kaczynski's Law and Justice (PiS), the main opposition Civic Platform (PO) and other parties say they are putting together campaign strategies and getting ready to select their candidates for parliament.

''We are preparing rules for setting up electoral lists and hope this will be approved on August 25 by our national council,'' Grzegorz Schetyna, a Civic Platform leader, said.

Despite fast economic growth, the biggest ex-communist European Union nation has been plagued by political infighting and rocky relations with its European partners since Kaczynski's Law and Justice party took power in 2005.

Kaczynski, a social conservative who promised Poles he would rid the country of sleaze, triggered the latest turmoil a month ago when he fired a junior partner, farm leader Andrzej Lepper, from the cabinet over a corruption investigation.

He has since sought to convince Lepper's rural Self-Defence party to abandon its leader and stay in the coalition, which would otherwise lose its majority in parliament.

But Self-Defence has rallied behind Lepper, who says he is innocent and has accused Kaczynski and his identical twin brother Lech, the president, of using dirty tricks to eliminate political opponents.

The war of words has further eroded support for the government. Surveys show many Poles have started to blame the prime minister for the political chaos and paralysis.

''The sense of dissatisfaction grows stronger with each and every day of the crisis,'' said Andrzej Rychard, a sociology professor at the Polish Academy of Science.

An opinion poll by the PBS institute today showed Law and Justice trailing the main opposition party, the pro-business Civic Platform, by 10 percentage points -- the biggest gap the institute has recorded for a year.

Other polls put the Civic Platform's lead at between 10 and 12 points.

STOP THE ROT The surveys illustrate the dilemma Kaczynski faces.

He could lose power in an early election, but prolonging the crisis and maintaining his rocky coalition could make him a lame duck and produce an even worse result for his party if elections were held at a later date.

He also risks his rebellious partners may play real mischief by joining forces with the opposition in parliament when it meets after the summer recess on Aug 22.

A senior Law and Justice source said the findings of the opinion surveys and the risk of losing votes in parliament were nudging the party towards calling an election in October or November, two years ahead of schedule.

The source said Kaczynski could agree to shorten the parliament's term, long sought by the opposition, at the August session of parliament.

''We are not keen on elections but it seems we cannot stop the processes which are underway,'' the source, one of Kaczynski's closest advisers, told Reuters. ''We certainly cannot allow the rot to set in.'' REUTERS GT HT1836