By Vicky Buffery
PARIS (Reuters) - Marine Le Pen's far-right National Front gave French President Nicolas Sarkozy's conservatives a fright on Sunday, snapping at the heels of the mainstream center-right in poorly attended local elections.
With 86 percent of votes counted, Interior Minister Claude Gueant said the president's center-right supporters had won 32.5 percent of the vote, with left-wing parties totaling 48 percent and Le Pen's anti-immigrant party polling 15 percent.
However, polling institutes said Sarkozy's own UMP party scored just 16 percent, barely ahead of the National Front. The interior ministry did not issue any separate score for the UMP.
The opposition Socialist party won about 25 percent with the hardline Left Front on 9 percent, ecologists on 8 percent and unaffiliated left-wing candidates with another 6 percent.
"This may be the best result we have ever recorded in cantonal elections, which are not traditionally favorable to the National Front," Le Pen said on France 2 television.
The vote showed people were turning their backs on decades of look-alike policies of center-right and center-left governments that had driven France into economic and social decline, she said.
The local elections, the last popular vote before next year's presidential election in which Sarkozy is expected to seek a second five-year term, confirmed Le Pen's breakthrough to stand neck-and-neck with other likely mainstream contenders.
The decisive second round of the departmental elections for some 2,000 local councilors will be held next Sunday.
Because the voting system favors alliances, the National Front is unlikely to win many seats since UMP leader Jean-Francois Cope reaffirmed that the mainstream conservatives would not back any far-right candidate.
Turnout in the first round was at a record low of 45 percent, according to the interior ministry.
One of the most unpopular presidents in recent history, Sarkozy has trailed left-wing rivals in opinion polls for months but he has now also fallen behind Le Pen in three surveys.
Typically, the National Front scores poorly in departmental elections, and Sunday's results were another indication that the far right is eating into Sarkozy's support due to exasperation over unemployment, living standards and immigration.
Marine Le Pen, elected leader in January, has given the party a less abrasive image than her father Jean-Marie, who was convicted of inciting racial hatred and minimizing the Nazi Holocaust.
While popular Socialist IMF chief Dominique Strauss-Kahn is keeping France guessing over whether he will run and Sarkozy has yet to formally announce his candidacy, Le Pen is already on the campaign trail. Her overtaking of Sarkozy has put conservatives on the defensive, insisting he is their best candidate.
Sarkozy's personal popularity ratings have slumped to around 29 percent in recent surveys taken before he put France in the vanguard of an international coalition to stop Libyan leader Muammar Gaddafi's forces attacking civilian protesters.
A CSA poll this month credited Strauss-Kahn with 30 percent support in the first round of a presidential election, with Le Pen on 21 percent and Sarkozy 19 percent.
A second, more recent Ipsos survey gave Strauss-Kahn 33 percent versus 19 for Le Pen and 18 percent for Sarkozy.
(Writing by Vicky Buffery, editing by Paul Taylor)