*

Government wants to raise retirement age by 2 years to 64

*

Railways, schools and refineries among those hit by strike

*

Unions say workers angry at inflation, conditions, pensions

*

Macron's reformist credentials at stake in dispute

*

Polls show widespread opposition to pension reform

By Michaela Cabrera and Ingrid Melander

PARIS, Jan 19 (Reuters) - Trains will grind to a halt in France on Thursday, classrooms will be shut and businesses disrupted as workers walk off their jobs in an attempt to derail a planned pension reform that would see the retirement age pushed up by two years to 64.

The nationwide day of strikes and protests is a major test for President Emmanuel Macron, but also for the unions.

Opinion polls show French voters overwhelmingly reject a reform that the government says is vital to ensure the pension system does not go bust.

The challenge for unions, which are far less powerful in France than they used to be, is whether they can transform that opposition to the reform - and anger with a cost-of-living crisis - into a mass social protest that would last beyond Thursday and eventually get the government to back-track.

"Inflation, working conditions, pensions ... (people) are fed up with all this and that's why we think many will join us," said Simone Legendre, a member of the CFE-CGC union that represents white-collar workers.

For Macron, what is at stake is his reformist credentials, both at home and with his European Union peers, as well as keeping public spending in check.

Pushing back the retirement age by two years and extending the pay-in period would yield an additional 17.7 billion euros ($19.1 billion) in annual pension contributions, allowing the system to break even by 2027, according to Labour Ministry estimates. Unions argue there are other ways to ensure the viability of the pension system.

Government spokesman Oliver Veran said the cabinet was "calm, determined" ahead of the strike and urged workers not to paralyse the country.

Unions have described the day as a starting point, with more strikes and protests to follow.

"What nobody can know, and even the unions don't know is whether French people are cross enough to ... block the country," said Sciences Po professor Bruno Palier.

The reform still needs to go through parliament, where Macron has lost his absolute majority but is hoping to get it adopted with the support of conservatives.

'NOTHING GOOD'

Public transport will be severely disrupted on Thursday.

Only between one-in-three and one-in-five high-speed TGV lines will be operating, with barely any local or regional trains running, the SNCF rail operator said.