Polls show most French voters think something must be done to keep the pension system from collapsing under growing debt. Unions say new money should come from elsewhere in the government budget, not from extending time in the work force.

For two decades, successive governments have made gradual moneysaving measures and lengthened working years, but ambitious changes, especially to public sector retirement packages, have often stalled amid widespread protest.

The retirement age “is not negotiable,” the head of the Workers Force union, Jean-Claude Mailly, said on France-2 television on Monday ahead of talks with Labor Minister Eric Woerth.

Mailly said his union would not “accept in one way or another being required to work longer.” He proposed raising the amount of money people pay out of every paycheck into the pension system instead.

The leader of the more moderate CFDT union, Francois Chereque, told reporters his union “is attached to the departure age of 60.” France is only slowly emerging from its worst recession in decades and labor relations are tense after waves of job cuts. Train drivers for the SNCF rail authority are in their sixth day of a strike, and laid-off workers north of Paris are holding negotiations with management Monday after threatening to blow up their auto parts factory.

The government has pledged not to reduce the amount of pension pay-outs, but Sarkozy has said that any other option will be considered - including raising the retirement age. Sarkozy said earlier this year that the pension reform will be his main project for the remainder of his presidential term, which ends in 2012.

While several other European countries have pushed the retirement age higher as life expectancy increases and baby boomers quit the work force, France has remained loyal to its 60-year limit.

The government is considering another option: raising the number of working years required to receive a full pension.

Currently 40 years are required for most professions, and that will rise to 41 in 2012, but could go higher in a new pension reform.

That too is a hot-button issue, and the most left-wing unions have pledged to resist such a move.

Unions are divided about how to respond to the government's plans, which the labor minister laid out in meetings Monday with union leaders and employers' groups.

The government will present its first draft pension reform proposal in May, finalize it in July for full Cabinet approval, and submit it to parliament in early September.

That means the final version will come out in the midst of the sacred French holiday season, when it is hard for unions to organize mass protests and strikes.

A poll released Monday showed that 56 percent of respondents oppose raising the retirement age, and 38 percent are ready to go on strike to defend it. The poll by TNS Sofres interviewed 1,000 people in person last Wednesday and Thursday.