Police used tear gas and water cannon against protesters in Paris

Thousands of public sector employees took to the streets in four major cities to demonstrate against the proposals, which would force them to work longer for a full pension.

There were clashes with police in Paris, who used tear gas and water cannon against protesters near the National Assembly building where Mr Raffarin was speaking.

To those who are afraid, to those who have fears, I say that our reform is a reform of national security Prime Minister Jean-Pierre Raffarin

Only a third of rail services were running nationwide, public transport was severely affected in several cities, and teachers walked out for the 11th time since the start of the school year.

But Mr Raffarin got an enthusiastic reception from centre-right members of the national assembly, some of whom stood and sang the Marseillaise.

"This is a necessary reform and everybody knows it," he said, pointing out that fewer people were paying into the pension system, as more were taking out of it.

Rubbish piles up

"It would be irresponsible to hide our heads in the sand like an ostrich," he said.

"It is lack of action which is putting the pension system in danger. Our reform will save it."

He added that without reform the pension system would be short of 43 billion euros ($50.4 billion) in 2020 and more than double that in 2040.

The existing reform plan would save 18 billion euros, he said.

Two leading unions have accepted the government's proposals, while four others agree that some reform is needed - but not the government's.

The pro-Communist CGT union has been on strike for a week, but on Tuesday several others joined in for the third nationwide strike in as many weeks.

Rubbish collectors were among those who stopped work, leaving waste piling up on doorsteps in some areas.

Air travel was less seriously affected than in previous strikes because the main air traffic controllers' union took no action.

High marks all round

At a meeting with teachers' leaders, the government gave some ground on the timing and scope of a plan to decentralise education, which is deeply opposed in the profession.

French commuters found alternative ways to travel

Some teachers have threatened to sabotage the end-of-year baccalaureat exams, which begin on Thursday, by awarding high marks all round or failing to turn up to supervise them.

Mr Raffarin on Tuesday warned them not to "take young people hostage".

The government's pension reform plan would oblige public sector workers to work 40 years to obtain full pension benefits, instead of 37.5 years, as at present.

RAFFARIN REFORM PLAN By 2008 public sector workers must work for 40 years to get full pension By 2012 all workers must work for 41 years to get full pension By 2020 all workers must work for 42 years to get full pension

This first stage of the reform would bring the public sector into line with the private sector, and would be completed by 2008.

The contribution period for all workers would then be increased to 41 years by 2012 and 42 years by 2020.

The government has said it wants the law passed before parliament's summer recess in July, but the left-wing opposition has promised it a rough ride.

The Communists have tabled more than 6,000 amendments.