By Dominique Vidalon
PARIS (Reuters) - France's ruling Socialist party is bracing for potentially heavy losses in mid-term local election on Sunday, a vote that could jeopardize reforms and hand major gains to the far-right National Front.
Voters will elect mayors in towns and villages across the country.
Dissatisfaction with President Francois Hollande's rule - his approval rate is at record lows of 19 percent in opinion polls - and a string of legal issues involving opposition conservatives are seen hitting turnout and helping the anti-immigrant Front (FN), which hopes to win outright in a record number of towns.
Prime Minister Jean-Marc Ayrault this week called on the opposition conservative UMP party to urge its voters to back Socialist candidates in towns where it stood no chance of election, promising the Socialists would do the same in a joint effort to keep out the FN out.
One Hollande aide forecast turnout of around 55 percent, about 10 points lower than normal, while recent polls have pegged it at around 60 percent.
"Abstention remains the main adversary of the left," Socialist deputy Jean-Jacques Urvoas told Le Figaro daily newspaper.
The abstention rate reached 33.5 percent in the last town hall elections of 2008, a record that many fear could be topped.
Two days before the first round, former president Nicolas Sarkozy, expected to run for re-election in 2017, injected himself into the campaign when he wrote in Le Figaro that judges who ordered the tapping of his phones were acting like secret police from ex-communist East Germany.
The comments prompted a backlash from Hollande who said comparing France to a dictatorship was "intolerable". It was unclear how Sarkozy's comments would impact voters' choices.
The election, opened to France's 44.5 million registered voters, is the first mid-term test for Hollande since he won the presidency in May 2012. Polls are due to open on Sunday from 8am to 6 pm (0700 GMT to 1500 GMT), with voting stations in big cities remaining open two hours longer.
Heavy losses for Hollande's Socialists could trigger a re-shuffle of the unpopular cabinet amid high unemployment and a sluggish economy and encourage backbench attacks of new pro-business policies on which Hollande has called a mid-year vote of confidence in his government.
Polls show the Socialists are favorite to hang on to Paris where the gaffe-prone efforts of the conservative candidate Nathalie Kosciusko-Morizet to lure so-called "bobo" (bourgeois-bohemian) voters have been widely derided on social media.
But the right-wing incumbent in Marseille, the UMP's Jean-Claude Gaudin, looks set to win a new term in France's second city as rival Socialist candidate Patrick Mennucci suffers from his links to an unpopular government.
The emergence under Marine Le Pen of the National Front as France's third political force adds unpredictability with many of the March 30 run-offs set to be three-way contests.
(Additional reporting by Mark John and Nicholas Vinocur Editing by Jeremy Gaunt)