* Socialist mayor Anne Hidalgo launches study of idea
* Conservative transport chief disagrees, cites tax burden
* Fares make up just 27 pct of Paris transport budget
* Transport could be key issue in 2020 mayor election
By Geert De Clercq
PARIS, March 20 (Reuters) - The mayor of Paris wants to make all public transport free in an effort to reduce air pollution, but faces staunch opposition from the head of the regional transport authority who said the move would hit taxpayers.
Socialist Mayor Anne Hidalgo announced plans late on Monday for a study into the feasibility of free city-wide transport, and told French daily Les Echos she wanted to debate the issue ahead of municipal elections in 2020.
Hidalgo said all the world's big cities were trying to develop clean mobility and boost air quality by reducing the number of cars on the roads, a goal that requires making public transport more attractive.
"To improve public transport we should not only make it more extensive, more regular and more comfortable, we must also rethink the fares system," she said in a statement.
But conservative politician Valerie Pecresse, head of the Ile-de-France region around Paris and president of the area's transport authority IDFM, rejected Hidalgo's proposal, saying if travellers did not pay, taxpayers would have to do so.
"Today, our priority is to modernise transport. Ticket sales bring in three billion euros ($3.7 billion) a year ... we need that money," Pecresse told Radio Classique.
Pecresse, who might challenge Hidalgo in the 2020 mayoral vote, said it would be unfair to make transport free for Parisians but not for people living in the suburbs.
Hidalgo did not spell out whether her proposal would cover just the 2.2 million residents of Paris or all 12 million living in the city and Ile-de-France region.
A 2015 study by Eurostat, the EU's statistics agency, showed Paris already has one of the highest levels of public transport use in Europe, with more than 60 percent of people using the metro, buses and train system. At the same time, a little over 25 percent of people said they use their car to commute.
IDFM has a 10 billion euro ($12.3 billion) annual operating budget, of which a little less than a third comes from passenger fares and the rest mainly from taxes including 42 percent from a transport levy paid by all firms employing more than nine staff.
Several smaller French cities already provide free buses.
Hidalgo referred to German plans for free public transport and said some European cities already have it, notably Estonia's capital Tallinn.
The German government is considering plans to make public transport free in cities suffering from air quality problems. It wants to test the measure in five cities including Bonn and Essen. http://reut.rs/2G6ykXf
Hidalgo has pushed through a series of measures to cut urban pollution, including turning highways along the Seine river into public parks and building more bike lanes. By 2020, Paris plans to ban all petrol and diesel-fuelled cars from the city centre. http://reut.rs/2hCJzs9
In recent years, Paris has imposed license plate-based driving restrictions to take up to half of the cars off the roads when pollution is at peak levels. http://reut.rs/2FXgVwO
Early last year it also launched a vignette system requiring all cars to have a color-coded sticker indicating their age and pollution level so it can impose more selective driving bans.
($1 = 0.8121 euros) (Reporting by Geert De Clercq Editing by Mark Heinrich)
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