* Turnout dips at marches but strikes set to continue
* Refinery strike weighs on airport, hits petrol stations
* Fresh protest on Tuesday to keep pressure on Sarkozy
(Adds fuel restarts to airport, detail on truckers, scuffles)
By Gerard Bon
PARIS, Oct 16 (Reuters) - A million or more people marched in cities across France on Saturday in the latest protest against President Nicolas Sarkozy's flagship pension reform, and refinery strikes squeezed fuel at airports.
The government said turnout was down significantly on a rally last weekend against the push to raise the retirement age, but unions said the numbers were stable and vowed to maintain pressure to drop the plans ahead of a Senate vote on Tuesday.
Only minor scuffles were reported during Saturday's marches, which came on top of five-day old rail and refinery strikes which have piled pressure on the centre-right government.
Jet fuel supply was restored to a key pipeline on Saturday, easing the pressure at Paris airports, but week-long strikes at all France's refineries could pinch supply hard from next week.
Truck drivers, the big guns of French protests, will start to block roads from Sunday evening, a union spokesman said.
But Labour Minister Erich Woerth, who is piloting the changes through parliament, said he thought the government's message was beginning to get through.
"The turnout is clearly down, but there are still a lot of people in the street," he said on i-Tele.
"I think the French people have understood that pension reform is essential and necessary," he said.
Sarkozy is determined to stand firm on his plans to raise the retirement age and stem a ballooning pension shortfall, but unions view the reform as unfair and have staged weeks of demonstrations to try to force him to back down.
France's CGT and CFDT unions said between 2.5 million and 3 million people joined street demonstrations from Toulouse to Rouen, down from the last weekend march on Oct. 2 and also from a Tuesday protest unions said was joined by 3.5 million.
The government counted 850,000 marchers, down from 899,000 on Oct. 2. The biggest crowds were in Paris, but the mood was upbeat with music blaring, horns honking and chanting. A few dozen arrests were made following minor disturbances.
A spokesman for France's civil aviation authority said the fuel flow through a key pipeline to Paris from northern France had been restored, meaning Charles de Gaulle international airport now has ample fuel until the end of next week.
An oil refinery strike which cut supply to the pipeline last week had left the airport looking earlier on Saturday at just two days' worth of fuel stocks. France's other main airport, Orly, has fuel reserves for several days.
POLICE ON ALERT FOR SCUFFLES
Unions have set their next big protest rally and nationwide strike for Tuesday, the day before a Senate vote on the pension bill, whose key clauses have already passed through parliament.
Open-ended strikes at France's 12 refineries since last Tuesday threaten to cause the government a huge headache if fuel dries up at France's main airports. Orly already had to ground some flights this week due to striking runway workers.
The CGT union coordinator for oil company Total, Charles Foulard, told Reuters workers at Total refineries would not return to work unless the government withdrew the pension bill: "There is toughening of resolve," he said. "The truck drivers are going to join us ... We will go till the end."
The refinery strikes, combined with unrelated strikes at Mediterranean oil ports and temporary fuel depot blockades, have hit supply at nearly 2 percent of France's petrol stations.
Economy Minister Christine Lagarde said only 230 out of a total 13,000 petrol stations were affected. The government says its fuel stocks would last the nation a month. "We have reserves," she told RTL radio. "People mustn't panic."
Sarkozy says his reform is the only way to stop the annual pension shortfall swelling to 50 billion ($70 billion) by 2020.
Lagarde told RTL that gradually lifting the minimum and full retirement ages by two years, to 62 and 67 respectively, would be less painful than raising pension contributions or trimming benefits for the 15 million people in France on pensions.
But unions are demanding a say in the pension overhaul.
"We have several million people in the street who support us and believe in us," said CFDT union leader Francois Chereque. "The only one blocking the country is the government."
French authorities were on alert for signs of violence on Saturday. Police in Paris had orders to not use rubber bullets, after a youth protester was injured by one during the week.
France has a tradition of overpowering unpopular government proposals through street militancy, though polls suggest people are coming to terms with the fact that delaying retirement, in line with other European countries, is becoming inevitable.
Unions will reconvene on Thursday to discuss further action. (Additional reporting by Patrick Vignal and Nina Sovich; Writing by Catherine Bremer; Editing by Jon Boyle)