PARIS, June 25 (Reuters) - The prospect of a politically

extreme party with little or no government experience taking

power after France's parliamentary elections is worrying

investors, the chief executive of Paris stock market operator

Euronext said on Tuesday.

The far-right National Rally (RN) party looks set to win the

most votes in snap parliamentary elections in the euro zone's

second-biggest economy on June 30 and July 7, with a left-wing

coalition called New Popular Front forecast to come second.

"If a team that has never governed comes to power, there is

total uncertainty, a complete unknown," Euronext CEO Stephane

Boujnah told France Inter radio in rare political comments.

As Marine Le Pen's eurosceptic, nationalist movement

appears closer to power than ever before, fuelling debates

across cafes, markets and workplaces, France's business elite

has kept largely silent.

Boujnah is the first well-known business figure to comment

on the election. No other chief of a major French company has

publicly expressed disquiet.

"There is also a lot of concern about other things that are

not economic, for example about what is happening to the unity

of French society and the risks that this unity, which could be

damaged, could have an impact on business," Boujnah added.

An IFOP opinion poll projected the RN would win 36% of votes

in the first round, ahead of the left-wing New Popular Front

(NFP) bloc on 28.5% and President Emmanuel Macron's centrist

alliance on 21%. France's voting system means the second round

can still deliver surprises.

'CIVIL WAR'

Seeking to cast their centrist camp as the last hope for

stability, Macron and his allies have turned up the volume on

warnings the country could face chaos if either of 'the

extremes' on the right or left wins power.

Finance Minister Bruno Le Maire has warned of a potential

financial crisis, while Interior Minister Gerald Darmanin has

said police were preparing for possible riots related to the

vote.

But surveys from all main polling institutes indicate the

strategy, reminiscent of the British government's communication

ahead of the 2016 Brexit vote dubbed 'project fear', is not

paying off. Macron's Together coalition remains well behind.

In the strongest comments so far, Macron said in a podcast

released on Monday that both the RN party and the New Popular

Front risked bringing "civil war" to France.

"The strategy of Mr Macron now is me or chaos," said Vincent

Martigny, political science professor at the University of Nice.

"He's playing a very dangerous game because he wants to

appear as a moderate, a stable point, but he is perceived as the

one who has been putting the French in such a messy situation."

RN leader Le Pen on Tuesday rebuffed Macron's allegations.

"I think the French have realised that the chaos is him

(Macron), he has embodied chaos since he was first elected," she

told RTL radio.

MARKET JITTERS

The president's surprise call for snap elections earlier

this month triggered a heavy selloff of French stocks and bonds.

France's economic model makes the country vulnerable when

interest rates attached to its sovereign and corporate bonds

shoot up, said Boujnah, whose company also runs stock markets in

other European hubs including Amsterdam and Milan.

"To continue to finance a system in which 58% of what we

create is injected into public spending, we have to borrow

heavily from the rest of the world. And we need the rest of the

world to give us loans," he said.

Investors and ratings agencies have raised concern about

RN's policies such as a pledge to cut value-added tax on energy

from 20% to 5.5% and to lower the legal retirement age.

So far, the party has been hesitant to put price tags on its

policies, despite promises it would keep France's state budget

within the boundaries agreed within the EU.

Jean-Philippe Tanguy, RN's financial pointman, on Tuesday

said the party's plan to reverse Macron's pension reform,

bringing the legal retirement age back to 62, would cost the

state 9 billion euros ($9.65 billion).

"It will be compensated by other measures", he told France

Inter radio, adding "our programme is balanced".

($1 = 0.9323 euros)