(Adds sales figures, minister's resignation)
By Brian Love
PARIS, Sept 4 (Reuters) - French President Francois Hollande's image took a new knock on Thursday with publication of a tell-all book in which ex-partner Valerie Trierweiler accused the Socialist leader of dismissively describing the poor as "the toothless".
Hollande ended his seven-year relationship with Trierweiler after his affair with an actress was revealed in January. The 49-year-old journalist vowed at the time that, breaking with a French tradition of maintaining discretion over private lives in politics, she would not keep quiet.
The 320-page book is laced with unflattering references to Hollande as cold or callous. But the charge that he ridiculed the poor was the one that sparked most media debate given his efforts to portray himself as aware of the plight of the needy.
"He presented himself as a man who disliked the rich," Trierweiler, a journalist with glossy magazine Paris Match, wrote of Hollande's successful 2012 election campaign.
"In reality, the president doesn't like the poor. In private, this man - the left-winger - calls them 'the toothless' and is so pleased at how funny he is."
On the day of its publication, Trierweiler's book shot to the top of Amazon.fr's bestseller list. It was also the strongest launch in five years for a book at FNAC superstores, where it sold three times as many copies as the first French edition of "Fifty Shades of Grey".
Hollande's Elysee Palace has refused to comment on the book. But, in an unexpected turn, it was Segolene Royal, the mother of Hollande's four children and the woman he left for Trierweiler, who sprang to his defence.
"This is the opposite of what he stands for," Royal, herself a former presidential candidate who is now his energy minister, told RMC radio, calling the accusation "total nonsense".
When he won power in 2012, Hollande, 60, marketed himself as a "Mr Normal" president whose car would stop at red traffic lights like everyone else's and said he would shun the bling-bling ostentation of conservative predecessor Nicolas Sarkozy.
While he this year took a more centrist course, he still insists that social justice is at the core of his government's policies.
Yet with the economy stuck in a rut and unemployment running at around 10 percent, his popularity rating has sunk to the lowest of any post-war leader at just 13 percent, a TNS-Sofres poll published in Le Figaro magazine showed.
In a further setback, Hollande's office said in a statement he had accepted the resignation of Thomas Thevenoud, a junior minister for trade appointed just nine days ago in a government reshuffle.
While Hollande's office cited personal reasons for the move, a source in Prime Minister Manuel Valls' office said it had to do with Thevenoud's tax situation.
"The Prime Minister considered that, in light of a situation discovered after Mr Thevenoud's nomination, he could no longer continue in his role," said another source close to Valls.
The Socialist government was shaken when ex-budget minister Jerome Cahuzac resigned in early 2013 after news website Mediapart revealed he had failed to declare funds kept in a Swiss bank.
RTL radio commentator Alba Ventura said that, true or not, Trierweiler's attacks risked being "devastating" for what was left of Hollande's public credibility.
Marine Le Pen, leader of the resurgent far-right National Front, accused Hollande and his former partner of sullying the authority of the role of president in the eyes of the public.
Trierweiler lived with Hollande at the Elysee presidential palace for a year and a half until a gossip magazine exposed his secret relationship with actress Julie Gayet, 42, in January.
In her book, titled "Thank You For This Moment", Trierweiler speaks of Hollande's coldness and mean-spirited stabs, and also says he attempted for months after the breakup to win her back, sending as many as 29 text messages in a day.
Hollande has shunned calls from some in his own party who believe his deficit-reduction strategy is being conducted at the expense of the economy and the needy, recently reshuffling his government to oust more hardline left-wingers.
His prime minister, Manual Valls, has called a confidence vote in parliament for September 16, where the scale of dissent within the ruling party - for now confined to a minority group of hardline leftists - may become clearer. (Writing by Brian Love; editing by Mark John)