Macron builds party machine and momentum before French election

* Macron's campaign taking off, polls show

* Former minister has built up a party machine

* En Marche! drawing support away from other parties

* Legislative elections also a target

By Michel Rose

PARIS, March 1 (Reuters) - Emmanuel Macron's spartan presidential campaign headquarters in western Paris is abuzz with rows of young recruits busy at their laptops.

Just two months ago the offices of En Marche!, the centrist party that has shaken up France's traditional left-right political scene since it was launched last April, were empty.

It now has 200,000 members and opinion polls show that 39-year-old Macron could become France's youngest leader since World War Two by nearly 10 years after the presidential election, expected to be decided in two rounds in April and May. He is also drawing support away from the mainstream parties.

"When you're in here I really feel like we're in a young political start-up. We do things completely differently," said Maelle Charreau, a political science student at En Marche's headquarters in the French capital.

"And then there's the personality of Emmanuel Macron which appeals to all of us here, his youth but also his political courage."

His supporters see him as a breath of fresh air in a political field full of seasoned insiders such as Socialist President Francois Hollande and The Republicains presidential candidate Francois Fillon, a former prime minister.

Fillon said on Wednesday he had been summoned by a judge to be placed under formal investigation following allegations he paid his wife for no apparent work. Fillon has denied the allegations but they have dogged his campaign.

Although admirers see Macron as something different, he graduated from the elite ENA school, a training ground for many French politicians and businessmen, before working in the finance ministry and becoming economy minister for Hollande.

He was also an investment banker at Rothschild, a factor which could make him vulnerable if he up comes directly against far-right anti-establishment candidate Marine Le Pen.

But with En Marche! membership swelling -- the Socialists are down 40,000 at 86,000 since the unpopular Hollande took office, The Republicans have 200,000 and there are 83,000 members of Le Pen's National Front -- Macron has also caught the eye of established politicians from other parties.

Socialists are careful not to alienate him and he was endorsed by veteran centrist Francois Bayrou.

Funding is also rolling in. Macron has raised 6 million euros ($6.35 million) so far, the same amount the Socialist party has put behind its candidate and near the 7.5 million The Republicans have. Spending is capped by law at 22 million.