By Chris Borowski and Pawel Sobczak
WARSAW (Reuters) - Polish Prime Minister Donald Tusk won a party leadership election with nearly 80 percent of the vote, but a stronger-than-expected showing by his challenger pointed to growing dissatisfaction in the party he co-founded.
Tusk's Civic Platform (PO) has trailed the main right-wing opposition party in most recent polls with a rising number of Poles unhappy over his handling of the economy, which earlier this year barely escaped its first recession in two decades.
The party has also suffered at the ballot box in local elections. Last month, PO lost an election for mayor of the city of Elblag, near Poland's Baltic Sea coast, that had been one of its strongholds. The party's deputy head, Hanna Gronkiewicz-Waltz, could be sacked as mayor of Warsaw in a vote in October.
Tusk was challenged by his former justice minister, Jaroslaw Gowin, who was fired in April after the two clashed over issues such as in vitro fertilization and civil partnerships for gay couples.
The party said on Friday Tusk won 79.6 percent of the votes cast by party members, his fourth straight victory in a leadership contest. Gowin took the remaining 20.4 percent.
But with turnout at just 51 percent, the vote was hardly the ringing endorsement Tusk had been hoping for.
Most observers had expected Tusk, who has maintained an iron grip on his party since ousting two other co-founders soon after it was launched in 2001, to win by an even wider margin.
"More than 20 percent for Gowin is a strong signal," said sociologist Andrzej Rychard. "A large part of his support is a reflection of dissatisfaction with Tusk."
Tusk had moved up the leadership election by nearly a year to quash internal bickering, which also came from the centrist wing led by former ally Grzegorz Schetyna, who decided not to challenge the prime minister.
Tusk congratulated Gowin for his "quite a good result" and asked party members to drop a motion to expel his former minister from the party for not backing a budget vote last month with two others.
Poland is not scheduled to hold a general election until late 2015, but the Civic Platform will face a strong opposition in next year's polls to pick local officials and representatives in the European Union parliament.
(Reporting by Pawel Sobczak and Chris Borowski)