A woman looks at Eugene Delacroix 's painting, "Liberty Leading the People (28 July 1830) (La Liberte guidant le peuple) in "La Galerie du Temps" (Gallery of Time) during media day on the eve of the inauguration of the Le Louvre Lens Museum, in Lens, northern France, in this December 3, 2012 file picture. REUTERS/Pascal Rossignol/Files

PARIS (Reuters) - A woman has defaced Eugene Delacroix's painting "Liberty Leading the People" with a black marker as it hung in an outpost of the Louvre gallery in northern France.

Police arrested a 28-year-old woman on Thursday for writing "AE911" across the bottom of a painting so closely identified with the French Republic that its image once graced the 100-franc note and it has been reproduced on postage stamps.

Painted in 1830, the work was on loan from the main Louvre in Paris to the new Louvre-Lens gallery in northern France inaugurated last December by President Francois Hollande.

"AE911Truth" is the name of a website called "Architects & Engineers for 9/11 Truth" whose backers say they are seeking to establish the truth of the September 11, 2001 suicide airliner attacks on New York's Twin Towers.

"It had really become an icon, a sort of symbol of the Republic which has remained famous throughout the ages," said Vincent Pomarede, head of the Louvre's painting department.

"We have a very passionate relationship with all our paintings and when something like this happens it's really hard to handle," he said.

Delacroix's "Liberty Leading the People" was painted after the 1830 July Revolution as a symbol of reconciliation following the overthrow of Bourbon King Charles X and the ascent to the throne of his cousin Louis-Philippe, Duke of Orleans.

The work, depicting a bare-breasted woman brandishing a tricolor flag and leading her people over the bodies of the fallen, was later adopted as a revolutionary emblem in the 1848 uprising which overthrew the Orleans monarchy.

It subsequently disappeared from public view before resurfacing in the Louvre after the advent of the Third Republic in 1871, after which its place in the French national consciousness was sealed.

The Louvre confirmed on Friday it had managed to save the painting as the black marker had not penetrated the upper layer of varnish and has been successfully removed.

Opened in December, the 150 million euro ($195 million) art center in Lens houses temporary exhibitions as well as a rotating collection of works from the Louvre museum in Paris.

It was conceived in an effort to regenerate a dreary northern region of France, once known for its mining industry, but now in economic decline.

While the Louvre in Paris looks out onto manicured lawns and flowerbeds of the Tuileries Gardens, Louvre-Lens sits on a disused coalmine and offers views onto slag heaps and a stadium housing the local football club.

(Additional reporting By Pierre Savary; Editing by Brian Love and Paul Casciato)