(Recasts adding Air France strike plan, economist quote)
* Sarkozy offers small concession as pension protests mount
* Air France unions announce 24-hour stoppage on Oct. 12
* More incremental amendments possible, depending on strikes
By Brian Love
PARIS, Oct 7 (Reuters) - President Nicolas Sarkozy sought to defuse union anger over his pension reform plans on Thursday with a concession to stay-at-home mothers, even as airline and energy workers prepared to join sweeping strikes next week.
Sarkozy, locked in a high-stakes battle with France's trade unions over his push to raise the minimum retirement age to 62, vowed to postpone the measure for women in their fifties who stopped work to bring up at least three children.
The adjustment to the pension bill before parliament would affect some 130,000 women, Labour Minister Eric Woerth said. Sarkozy's office said the tweak would cost 3.4 billion euros ($4.8 billion), to be financed by a rise in capital gains tax on property sales.
"This is in line with our view that the government has some pre-set margins for manoeuvre for negotiations, and suggests it is aiming to avoid a repeat of 1995," said Barclays Capital economist Laurence Boone, referring to paralysing strikes that forced former Prime Minister Alain Juppe to abandon his attempt to reform pensions.
Rather than taking the gesture as a reason to back down, one major union said it showed ground could be won through protests.
On the defensive on multiple fronts and grappling with a slump in popularity ratings ahead of elections in 2012, Sarkozy now faces a fifth round of potentially crippling pension protest strikes next week.
The government says the legislation is vital to ease a swelling deficit in the pay-as-you-go pension system, curb rising public debt and safeguard France's coveted AAA credit ratings, which let it borrow at the lowest market rates.
Families, students and private sector employees have already joined protests across the country and disrupted transport in four waves of strikes in as many months. A partly-related oil port strike spread on Thursday to refining plants.
UNIONS CHEER PENSION CONCESSION Unions at the state railways, Paris's urban transport network and in the energy sector have called rolling strikes from Tuesday, and on Thursday unions at national carrier Air France-KLM called for a 24-hour walkout.
Sarkozy has vowed not to back down on the essentials of his bill, namely a gradual increase in the minimum retirement age to 62 from 60 by 2018. The age at which people can retire on a full pension is set to rise to 67 from 65 by 2023.
Prime Minister Francois Fillon says that without the reform, the pension system would bleed 45 billion euros a year by 2020, derailing attempts to slash France's budget deficit to the EU limit of 3 percent by 2013 from a forecast 7.7 percent in 2010.
Woerth told the Senate that around 130,000 mothers would benefit from the amendment proposed on Thursday, which would postpone for five years the increase in full pensionable age in the case of women born in the early 1950s who gave up jobs to look after at least three offspring or a handicapped child.
"This shows that ... taking to the streets can lead to changes in a text that had been presented as perfect," Bernard Thibault, national leader of the CGT union, said.
The pension reform has been approved by the lower house National Assembly and is now working its way through the Senate.
Jean-Pierre Bel of the opposition Socialists slammed the measure as disingenuous. "This announcement has been staged to make it look as though something has changed," Bel said.
"The government is embarrassed and can see that the protest is not waning, so they've decided ... to deploy what to me is more of a smokescreen than any genuine progress on the issues people are protesting about," he said.
In a local but related dispute, dockers at the largest oil terminal in France, Fos-Lavera, kept dozens of tankers waiting offshore in a strike that entered its 11th day. Attempts to start strikes at nearby oil refineries met limited success, with just one in four plants voting to walk out. (Additional reporting by Dan Flynn, Clement Guillou, Laure Bretton and Muriel Boselli; Writing by Catherine Bremer; Editing by Ruth Pitchford)