The the second round of balloting will see the election of 4,108 local councilors who have limited powers over roads, schools and social services

The vote is not normally the focus of much attention in France. This time, however, the challenge posed by the anti-immigrant, anti-EU National Front under Marine Le Pen (center in photo above) has made the election a litmus test for the popularity of the two main parties.

Although the conservative UMP party of former President Nicolas Sarkozy is expected to dominate Sunday's runoff after its victory in the first round last week, the National Front, which won 25 percent of the vote to come second last week, is thought likely to increase its growing hold on grassroots politics.

Eight candidates from National Front were elected in the first round, in comparison with the two councilor positions it currently holds, and an Ifop poll has suggested 100-120 more could be elected this time round. The party came in first in EU elections last year in France.

The Socialist party of President Francois Hollande poses little threat to the UMP's ascendancy, with its popularity hitting all-time lows in recent months.

Prime Minister Manuel Valls has called on Socialist voters to cast their ballots for Sarkozy's conservatives on Sunday in a bid to block the National Front as parties jockey for position ahead of the 2017 presidential race.

Sarkozy, for his part, will need a big win to consolidate his place at the helm of the UMP and gain its nomination as presidential candidate.

Opinion polls have shown that the UMP and its allies are likely to take nearly twice as many seats as the Socialists and their partners.

In the French local election system, two councilors are chosen per constituency, who then vote to decide on 98 presidents of departement assemblies. This means that it will not become immediately clear how many departements each party has won.

Both of the main parties have ruled out joining forces with the National Front to chair a departement.

tj/sms (Reuters, dpa)