By Michel Rose and Leigh Thomas
PARIS (Reuters) - France's mainstream political parties were scrambling for a way to stop the rise of the far-right National Front (FN) on Monday after it emerged with an historic first-round lead in regional elections.
Boosted by fears over the Islamic State attacks that killed 130 people in Paris on Nov. 13, by record unemployment and worries about immigration, Marine Le Pen's party secured 27.7 percent of the vote nationally. It came first in six of 13 regions in Sunday's vote, the best showing in the history of the anti-Europe, anti-immigration party.
Riding a wave of mounting euroskepticism and anti-immigrant feeling across Europe which has brought far-right parties to prominence, the breakthrough bolsters Le Pen's position as a serious contender for the 2017 presidential election.
It also exposed fault lines within both the country's main traditional political groupings over the right tactics to confront the National Front in the decisive second round of the regional elections next Sunday.
Le Pen is not assured of winning in any regions in the final round. To try to make sure she does not, France's ruling Socialist Party decided to pull its candidates out of three regions where it came third, telling supporters there to back Nicolas Sarkozy's conservative Republicans.
But many in President Francois Hollande's party are unhappy about giving up all regional representation across swathes of the country, and on Monday, Jean-Pierre Masseret, who leads the Socialists in the eastern region, resisted calls from his party chief to pull out.
"We are standing fast. We think the best way to oppose the National Front is by taking our seats in the regional assembly. That is where we can best push back the National Front, by being the opposition," he said on BFMTV.
Sarkozy has ruled out a similar tactic by his own party, and a meeting on Monday validated that position, but some of his allies believe he should copy the Socialists' strategy.
"When you are third, you pull out. You create a front against the destructive force because now is the time to rebuild," said former prime minister Jean-Pierre Raffarin, who is from the centrist rank of the party.
Le Pen is riding a wave of disillusion with mainstream politics and the Socialist government's failure to tackle unemployment, stuck at above 10 percent. Its anti-immigration stance and calls for tighter national security have also found a focus after the Nov. 13 attacks.
Long the pariah of French politics, the FN has won greater respectability since Marine took over from her father Jean-Marie as head of the party in 2011.
Le Pen senior was thwarted in his bid for the presidency in 2002 when the Socialist Party used a similar tactic to the one they deployed on Monday. Its own candidate, Lionel Jospin, was knocked out in round one, so it urged supporters to prevent a Le Pen win by voting for Conservative Jacques Chirac, who won with more than 80 percent of the vote.
On Monday, Marine Le Pen was careful not to claim victory, and also denounced the Socialists' tactics as anti-democratic.
"We're not home and dry yet, especially since the election is being run in an unfair way," she told French radio RTL.
"To pull out a candidate on the second round is rather unfair. Today, they're twisting the arm of the French, of the left. Are they going to accept being insulted, despised? We'll see," she said.
The National Front won 27.73 percent of the first-round vote nationwide, according to final official figures. The Republicans and its allies won 26.65 percent and the Socialists 23.12.
Le Pen won 40.64 percent of the vote in the Nord-Pas-de Calais region she contested and her niece Marion Marechal-Le Pen scored 40.55 percent in Provence-Alpes-Cote D'Azur in the south. The abstention rate was 50.9 percent nationally.
(Writing by Andrew Callus; Editing by Janet Lawrence)