* Company wants to focus on growing top brands online
* Looking to sell 10 titles, including Be and Psychologies
* Titles that can't be sold will be closed - internal memo
* Restructuring puts at least 350 permanent jobs at risk (Adds detail from internal memo, union representative comments)
PARIS, Oct 17 (Reuters) - Media group Lagardere said it planned to sell 10 magazine titles to focus on growing its most strategic brands online, such as the French edition of "Elle", in a restructuring that threatens hundreds of jobs.
Titles for sale include popular Psychologies Magazine, Be and Premiere, and several home and decoration magazines, Lagardere Active said in a statement on Thursday.
If the titles did not find buyers, they would have to be closed and around 350 permanent jobs would be lost, according to an internal memo seen by Reuters. A union representative said more than 500 jobs were at risk.
Like many media groups, Lagardere Active has been hurt by a significant drop in circulation and advertising revenue in its print publications as it faces soaring competition from content available at little or no cost on the Internet.
Lagardere Active, which already sold its international magazine portfolio for around $900 million to U.S. publisher Hearst in 2011, said it aimed to focus on the digital development of its most powerful brands, including the French edition of Elle, Paris Match and Le Journal du Dimanche.
"My strategy is to focus our investments on around 10 titles which are leaders in their segment and where there is a strong potential to develop them online," Lagardere Active head Denis Olivennes said in an interview with Le Monde newspaper.
The restructuring will affect 350 permanent jobs, mostly staffers at the magazines being sold, he said. He added that the company preferred for the titles to be taken over by their individual teams and that he hoped employees would be retained.
But in a separate letter to staff, of which Reuters saw a copy, he said: "If - and this is not how we see things - we did not manage to sell some of these titles, we would have no other choice but to close them."
A labour union representative, who attended a meeting with management earlier in the day, said the figure of 500 jobs would be reached when freelancers were included.
"We're all pretty shocked. It adds up to a lot of people," SNJ union representative Christian Legueil told Reuters.
Lagardere shares were little changed at 25.47 euros by 1507 GMT. They are up about 46 percent this year, giving the company a market value of some 3.3 billion euros ($4.45 billion).
Lagardere said in August it expected advertising revenue to fall about 7 percent at Lagardere Active this year.
The magazine and radio division accounts for roughly a fifth of the group's revenue.
"Let's not bury our heads in the sand... the press is on the verge of heart failure and we must resort to shock therapy," Olivennes told Le Monde. ($1 = 0.7412 euros) (Reporting by Natalie Huet; Editing by James Regan)