By Ingrid Melander and Elizabeth Pineau
PARIS (Reuters) - A revolt by 100 members of French President Emmanuel Macron's governing party has exposed tensions in the fledgling movement as it prepares to elect a leader handpicked by him on Saturday.
Created about 18 months ago when Macron was still relatively unknown, En Marche's membership has risen quickly to 360,000 -- membership is free -- but retaining members could be harder as his popularity has waned following his rise to power.
The activists who quit this week said the party that helped Macron, a centrist, triumph in this year's presidential election and then won a parliamentary majority had become less open and lost its appeal as a movement that would do things differently.
The number of defectors is small, and none is a lawmaker, but their complaints underline the challenges 51-year old government spokesman Christophe Castaner will face as party chief.
"We need to reinvent our political movement," Castaner, the only candidate, told party members ahead of Saturday's party congress. "That is key to accompany the reforms carried out by the government and parliament."
A Socialist for about three decades until he backed Macron's election bid, and a former lawmaker from southeastern France, Castaner will aim to change what opinion polls show is Macron's image of a "president of the rich."
He will also set out to transform En Marche (LREM) into a more established party with the strength and depth required to compete in the next local and national elections.
The next ballot, for the European Parliament, is in 2019 and local elections will be in 2020 at the earliest.
ARROGANCE, LACK OF DEMOCRACY
Although mocked as an empty shell by rivals from long established parties, En Marche attracted many newcomers to politics and quickly proved effective in propelling the former economy minister of Socialist President Francois Hollande into the presidency.
Supporters set up more than 3,000 local committees across France in the months leading to the presidential election, helping make up for Macron's disadvantage of not having an army of elected officials to promote his candidacy.
But some of those who joined En Marche with high hopes now say there is a lack of democracy in the party.
"Castaner's election shows an autocratic way of doing things," said Tiphaine Beaulieu, one of the members who quit this week and issued a strongly worded statement condemning what En Marche has become.
Complaining that Castaner is the only leadership candidate, she said arrogance and a lack of democracy were now features of how the party worked.
Opposition parties have also criticised En Marche, and taken Macron to task over the fact that Castaner may keep his role as junior minister for relations with parliament when he becomes party chief.
"So the new world according to Macron is choosing (your party leader) alone in your Elysee office," Socialist lawmaker Luc Carvounas wrote on Twitter, referring to the president's official residence, the Elysee Palace in Paris.
Forty-eight percent of voters trust Macron with pursuing the right policies for France, a Harris Interactive poll showed last month, a drop from 57 percent in the same survey when he was elected in May.
En Marche officials say that over the last six months, En Marche has gained about 160,000 new members, so the loss of 100 activists is not a significant number.
"Once the euphoria of victory has passed, it is quite normal that some may have the blues a bit," said Laurent Saint-Martin, a 32-year old lawmaker who was not involved in politics before he joined LREM.
"But activists are still here. The question is simply how we work together," he said. "The party was built for the presidential and parliamentary election, many have left to become lawmakers or work in government, so it is normal that we should reconstruct it."
(Writing by Ingrid Melander, Editing by Michel Rose and Timothy Heritage)