PARIS (Reuters) - French Socialist would-be presidential candidate Manuel Valls on Friday criticized conservative rival Francois Fillon’s proposals to slash public payroll and health spending, saying they threatened the foundations of a welfare state dear to voters.

Francois Fillon, member of Les Republicains political party and 2017 presidential candidate of the French centre-right, attends a lunch during a visit in Chantenay-Villedieu, western France, December 1, 2016. REUTERS/Stephane Mahe

Valls’ salvo came on the heels of an opinion poll showing 90 percent of people opposed to cutting spending on public healthcare - a Fillon proposal that is raising concern even in his own party, the center-right Les Republicains.

“Things can be reformed, new sources of financing found... but you can’t talk about the public service like that, eliminate 500,000 jobs, privatize social welfare, end reimbursement of healthcare costs for a whole list of illnesses,” Valls said.

Valls stood down last week as prime minister and hopes to secure the Socialist Party ticket in a primary next month to enter next year’s presidential contest, which all current polls indicate Fillon will win.

“This is what France is about: social welfare, healthcare, aid for the most vulnerable, pensions -- the pillars of the social contract,” Valls told BFM TV in an interview.

Far-right National Front leader Marine Le Pen echoed those comments.

“Doctor Fillon is prescribing for us an American-type ultra liberal remedy where the rich will have the means to cure themselves, the poor will benefit from the most meager healthcare and where families and the middle classes will be most sacrificed,” she said in a speech.

At issue are a few lines in Fillon’s election program that drew little attention until he became the candidate for Les Republicains at the end of November.

In the manifesto, the former prime minister says that the public healthcare system has scarcely changed since it took shape in 1945, and cannot continue to operate under debts of 110 billion euros ($117 billion).

“I propose a system of general public insurance focused on serious or long-term illnesses, with the rest privately insured,” he writes.

Even people from his own party are worried.

Bernard Accoyer, secretary general of Les Republicains and traditionally close to Fillon, called this week for clarification, something Fillon’s aides have said he will do soon.

His room for back-pedaling is limited, though. One of the central themes of his campaign has been that governments must break their habit of promising one thing and then doing another once elected.

His program involves cutting public spending by 100 billion euros, cutting 500,000 public sector jobs, and pushing the work week back up to 39 hours from 35 currently.

France’s healthcare system is financed by taxes collected from workers and employers; the social security system reimburses the cost of most medicines, doctors’ fees and treatments.