* Campaigning stops before presidential vote on Sunday
* Voters disillusioned, high abstention rate seen
* Campaign marked by frivolous, symbolic proposals
By Daniel Flynn
PARIS, April 21 (Reuters) - France's presidential candidates observed a one-day truce on Saturday on the eve of a first-round vote expected to send President Nicolas Sarkozy and Socialist challenger Francois Hollande through to next month's runoff.
Final polls before a mandatory media blackout on campaigning from midnight on Friday showed Hollande narrowly ahead of the conservative leader for Sunday's first-round vote but the comfortable winner of the second round on May 6.
Voting began on Saturday in French overseas territories, including the north Atlantic islands of Saint Pierre and Miquelon just off the coast of Canada.
Many of the 44.5 million registered voters have complained about a lacklustre campaign, and the prospect of a record abstention looms over Sunday's vote in mainland France.
On the streets of Paris, disappointed voters said the main candidates had ignored the pressing challenges facing their country, including unemployment running at a 12-year high and gloomy economic prospects.
"The campaign has not been serious enough. The important issues have not been discussed," said Frederic Le Fevre, a self-employed businessman. "They've focused on childish arguments, throwing blame at each other."
Candidates argued for weeks about halal meat and the cost of a driving licence. Even the leading contenders tried to win the limelight with largely symbolic proposals, like Hollande's plan to scrap the word "race" from the constitution and Sarkozy's offer to bring monthly pension payments forward by eight days.
An Ifop poll in early April suggested that 32 percent of registered voters might not bother to vote in the first round.
Hollande, mindful of an upset in 2002 when far-right candidate Jean-Marie Le Pen knocked out Socialist Lionel Jospin in the first round amid the highest-ever abstention rate, warned supporters against complacency at a closing rally on Friday.
"It's the sixth of May when we will have a president but April 22 will decide the dynamic one way or another," he said.
After trailing Hollande for months, Sarkozy edged ahead in first-round voting intention polls for a few weeks, helped by his strong response to a shooting spree by an al Qaeda-inspired gunman who killed seven people in southwest France last month.
He lost that lead in the last week before the election, and polls on Friday showed Hollande winning the first round by 28 percent to 27, and taking the second by 55 percent to 45.
It would be the first time in France's Fifth Republic, founded in 1958, that an incumbent president has not finished top of the first round.
Polls in mainland France were due to open on Sunday from 8 a.m. to 6 p.m. (0600 to 1600 GMT), with voting stations in big cities remaining open two hours longer.
The first official results will be released after the last voting booths close at 8 p.m.
Hollande, who has promised to raise taxes on large corporations and people earning more than 1 million euros a year, would be France's first left-wing president in 17 years.
With the euro zone in crisis, that prospect has placed the strained finances of the bloc's No. 2 economy in the spotlight.
The risk premium investors charge for holding French 10-year bonds over German Bunds rose above 1.50 percentage points on Friday in a possible foretaste of market jitters over an Hollande victory.
Traders think he may face pressure to go beyond his centre-left programme if a resurgent hard left makes gains in June parliamentary elections and holds the balance of power.
Hollande was catapulted to the Socialist candidacy by the arrest of former IMF chief Dominique Strauss-Kahn in New York in May on charges of sexually assaulting a hotel maid. Strauss-Kahn was cleared of criminal wrongdoing but remains mired in an investigation into a prostitution ring in France.
Frustration with Hollande's bland manner and Sarkozy's flashy style has allowed more radical candidates to flourish.
National Front leader Marine Le Pen is running third on 16 percent, a fraction below the vote achieved by her father Jean-Marie when he shocked France by reaching the second round in 2002.
Far-left candidate Jean-Luc Melenchon, a Communist-backed firebrand, has stormed into fourth place with around 14 percent, captilising on frustration at economic stagnation and an anti-capitalist backlash against the world of finance.
Under the banner "They do not represent us", left-leaning protesters from towns across France were due to hold a march in central Paris later on Saturday.