PARIS (Reuters) - France deployed hundreds of police in Paris on Monday to enforce the most drastic curbs on car use in 20 years as authorities sought to reduce health-endangering pollution days before town hall elections.

Amid concerns of worsening air quality after a week when unseasonably balmy weather boosted pollution, public transport was free of charge while drivers with even-numbered license plates were told to leave their cars at home of face fines.

Paris is more prone to smog than other European capitals because of France's diesel subsidies and its high number of private car drivers.

Some 700 police manned key entry points to the city from before dawn to apply the scheme, in which drivers may only use their cars on alternate days depending on whether their license plates finished with an odd or even number.

"This is a public health problem . . . and we thank everyone who has fallen into line," Transport Minister Frederic Cuvillier said, adding that early results showed traffic tailbacks had been shrunk by 60 percent in the Monday morning rush hours.

While nowhere near levels seen in some Asian cities, European Environment Agency (EEA) figures showed last week 147 micrograms of particulate matter (PM) per cubic meter of air in Paris - compared with 114 in Brussels, 104 in Amsterdam, 81 in Berlin and 79.7 in London.

The last restricted driving scheme was introduced in 1997 in to combat pollution from heavy diesel fumes. It lasted one day.

Minister Cuvillier said a decision would be taken later on Monday on whether to extend the driver curbs for a second day.

Early reports suggested police were applying the curbs with a degree of flexibility, with exemptions allowed for many categories of vehicles including taxi cabs and hybrid cars.

"It's not our goal to jam up economic activity," Thierry Pujol, a police officer stationed at a checkpoint in southern Paris, told BFM TV. He said his team had stopped about 150 vehicles early in the day, waving many delivery vans through and fining about 30 of the drivers stopped.

Drivers who defy the curbs are fined 22 euros ($31) on the spot. The anti-smog action is being implemented days before voters elect city hall mayors across the country in a two-round ballot on March 23 and 30. Polls show President Francois Hollande's Socialists are favorites to retain control of the French capital.