PARIS, Feb 5 (AFP) - Hundreds of thousands of French people took part in demonstrations across the country Saturday to protest against government plans to reform the 35-hour work week.  

Organised by an alliance of trade-unions and backed by the opposition Socialist party (PS), more than half a million people took part in marches in 100 towns and cities - with 90,000 joining the largest demonstration in Paris. Police put the overall figure at slightly more than 250,000.  

The protests came as a bill to enable private sector employees to opt for longer hours makes its way through parliament. The bill is expected to pass its first reading in the National Assembly on Monday.  

The key social change of the last Socialist administration, the mandatory 35-hour week has been attacked by President Jacques Chirac's centre-right Union for a Popular Movement (UMP) for putting up the cost of labour and helping create the country's stubbornly high unemployment.  

However the left accuses the government of trying to turn back the clock, and jeopardising social progress via an ideological obsession with labour market flexibility.  

Polls showed that nearly 70 percent of the public support or have sympathy with the protests, which come after three days of strikes in the public sector late last month.  

The left-wing opposition is seeking to build on public discontent about low pay and joblessness to mount a concerted campaign against the government's economic policies, which it says are driven by the interests of business and not of ordinary workers.  

However the left is itself divided about how hard to push the campaign. Many fear that it could merge with the growing opposition to the EU's proposed constitution - which union and Socialist leaders are pledged to support at a referendum later this year.  

"I see a lot of anger out there about the fall in disposable income, a lot of unhappiness about how the government won't listen, and a lot of people mobilising in the hope of a change of power in 2007," said PS leader Francois Hollande at a demonstration in the western city of Rennes.