PARIS (Reuters) - A French prosecutor opened a preliminary investigation after a mayor was recorded telling a group of itinerant Roma parked illegally near his town that Hitler had not killed enough of them.

Gilles Bourdouleix, who is also a lawmaker for of the centrist UDI party, made the comments during an altercation with the group, which had parked more than 100 cars on a field near Cholet, local media reported.

His remarks were broadcast across France as President Francois Hollande moves to defuse growing anger over illegal Roma camps from conservatives and frustrated taxpayers, who, in a time of austerity, feel that social services provided by the state are being abused.

On a recording posted on various media websites, Bourdouleix could be heard saying "Hitler maybe didn't kill enough of them".

But the mayor told a television channel his comments had been misinterpreted.

"I mumbled something like, 'if it was Hitler he would have killed them here', meaning, 'thank goodness I'm not Hitler' and so there's no reason to call me Hitler," he told BFM news TV. "This is shameful score-settling which aims to smear me."

He was not immediately available for comment to Reuters.

"This is not a slip of the tongue," Interior Minister Manuel Valls told news channel i>Tele TV.

"A case has been brought before the courts because this is praise for the crimes of World War Two. It's praise for Nazis, and coming from a mayor it's unbearable," he said.

Angers prosecutor Yves Gambert later confirmed that a preliminary investigation had been opened into whether Bourdouleix was an "apologist for crimes against humanity".

A person found guilty of such a crime can face up to 45,000 euros ($59,500) in fines, a year in jail, or both.

Last week, Hollande's Socialist Party proposed a law making it easier to evict itinerant groups, amid worries that the issue could prove damaging to his unpopular government in municipal elections one year from now.

About 250,000-300,000 itinerant Roma live in France, most of them French citizens. They have a special status that allows them to park their mobile homes temporarily in designated open-air areas with power and water hook-ups during the summer.

The head of the UDI, Jean-Louis Borloo, said he would seek to exclude Bourdouleix at the next meeting of the party's executive committee, according to media reports.

Under Hitler's rule, Nazi Germany attempted to exterminate the Roma people of Europe. Estimates of how many were killed in Nazi concentration camps range from 220,000 to 1,500,000.

(Reporting By Chine Labbe; Writing by Nicholas Vinocur and Alexandria Sage; Editing by Raissa Kasolowsky and Andrew Heavens)