Dock workers also walked off the job over plans to privatize part of their industry, underscoring the difficulties faced by President Nicolas Sarkozy as he tries to modernize the economy and reduce state spending.

In a rare show of unity, France's eight largest unions called on workers to take to the streets in dozens of cities to oppose the government's decision to require employees to work 41 years before retiring against 40 years at present.

"Forty years is already too long," protesters chanted at the start of the biggest rally, in Paris.

"We don't want to die at work!" others shouted.

The CGT, the largest union, estimated that more than 700,000 people had taken part in 153 demonstrations across the country. Police put the figure at just under 300,000.

"The mobilization in favor of a pensions system based on solidarity is unquestionably a success," the CGT said.

More than a million people took to the streets during the last such demonstration against pension reform in 2003, and last November transport workers staged a nine-day strike against plans to scrap special pension rights for state sector workers.

But there appeared to be little appetite for a full blown strike this time.

Public transport in the two main cities, Paris and Lyon, was little affected, most major rail links were running and very few flights were delayed out of the airports.

PORT BLOCKADES

Many ports were paralyzed though, hit both by a 24-hour strike by workers fighting against plans to privatize part of the state docks system and by fishermen up in arms over the rising cost of fuel that has wiped out their profit margin.

A year after Sarkozy was elected on a platform of sweeping economic reforms, his approval rating has tumbled because of concern over the rising cost of living and disapproval over his abrasive, sometimes flashy, style of government.

Unions hope to tap into this discontent and force a U-turn over pensions. But the government says that rising life expectancy coupled with weak public finances means the pensionable age must rise, as it has elsewhere in Europe.

"We're protesting so that on the one hand we will be able to live off our pensions in the future, but also so that they will allow our children to live," said Georges Sarda, 65, who was on the Paris march and who retired five years ago.

Looking to appease union anger, the government has committed to keeping the minimum retirement age to 60 against 65 in many of its neighbors, including Britain and Italy.

Opponents say the real problem is that many firms lay off workers in their 50s, who then collect benefits until they can retire, and urge the government to tackle this problem first.

Sarkozy has shown little sign of backing down over pensions, but has shown more sympathy towards France's 24,000 fishermen, who say their fuel costs have doubled in a year.

The government on Wednesday offered them 110 million euros ($173 million) in aid for 2008 -- a proposal accepted by the main fishing association but rejected by many trawler crews who maintained their blockade of numerous ports.

(Additional reporting by Gerard Bon, Jean-Baptiste Vey, Tamora Vidaillet; Editing by Estelle Shirbon)