By Natalie Huet and Elizabeth Pineau
PARIS/LA ROCHELLE France (Reuters) - French Prime Minister Manuel Valls was jeered on Saturday on the way to his Socialist Party's end-of-summer gathering, where attacks on the government's pro-business economic policy highlighted an uncomfortable divide within France's left.
Stepping off the train in the western port town of La Rochelle, booed by left-wing militants and unionists, Valls said it was healthy for a party to debate policy, but warned that Socialists needed to stand united or risk losing voters.
Valls reshuffled his cabinet on Tuesday, evicting rebel leftist ministers who had urged President Francois Hollande for an economic policy U-turn away from budgetary rigor, and further angering many on the Socialist party's left wing.
The shake-up raises the risk that the ousted rebels - including maverick former economy minister Arnaud Montebourg - could have enough allies in parliament to deprive the government of the majority it needs to implement reforms. Valls has said he would submit his cabinet to a parliamentary vote of confidence in September or October.
"Everywhere possible, we need to have an alliance, to bring together the nation's forces. And this is first and foremost necessary on the left and among Socialists," Valls told reporters upon his arrival in La Rochelle.
Earlier on Saturday, Justice Minister Christiane Taubira, from the junior coalition Left Radical Party and one of the last leftist members of the new Valls government, joined a meeting of rebel Socialist lawmakers and criticized the Socialist Party for letting the French "lose faith in their future".
Valls said he had no problem with Taubira, had come to the traditional end-of-summer gathering in "a constructive spirit" and would give a speech before his fellow Socialists on Sunday.
However, he noted that the nation had lately vented "anger and frustration" in the polls and suggested the Socialists stop bickering or lose even more voters. France's ruling party suffered a drubbing in March municipal elections and the far-right National Front came out leaders in EU elections in May.
"Socialists are strong... when they address the French, not when they're only talking among themselves," Valls said.
Yet shortly after, former Socialist Party chief Martine Aubry chimed into the debate. In a statement, the mayor of Lille urged Valls to let cities like hers enforce rent caps, instead of restricting them to Paris as part of a house-building stimulus plan he unveiled on Friday.
National Front leader Marine Le Pen ridiculed the Socialists' constant bickering and said she did not see the new Valls government lasting more than just a few months.
"Francois Hollande the king has no clothes, but neither has Prince Manuel Valls, forced to put together a new government when the previous one didn't even survive the summer. And the new one won't survive the fall or the winter either," Le Pen told a meeting of National Front supporters in eastern France.
Le Pen reiterated her party's call for a parliamentary dissolution, saying she was confident it could win early elections and stood ready to govern.
(Reporting by Natalie Huet in Paris and Elizabeth Pineau in La Rochelle; Additional reporting by Gregory Blachier in Paris; Editing by Rosalind Russell)