PARIS, Sep 30 (Reuters) The head of France's Socialists, Francois Hollande, pulled out of the race to head the party's challenge in next year's presidential election, a day after his partner, front-runner Segolene Royal, said she would run.

''I will not be a candidate because I am at the service of my party and not the other way around,'' Mr Hollande told the regional newspaper Dauphine Libere in an interview in today's edition.

The decision by Hollande, the party's First Secretary, narrows the Socialist field further after former Prime Minister Lionel Jospin dropped out on Thursday.

So far Royal, who dominates the other left-wing candidates in the opinion polls, and former Finance Minister Dominique Strauss-Kahn have said they will run.

Laurent Fabius, prime minister under France's last Socialist President Francois Mitterand and former Culture Minister Jack Lang are expected to announce their candidacy before an October 3 deadline.

The race for the Socialist nomination, which has been running unofficially for months, has opened up personal and political divisions that many in the party fear could help the right's likely candidate, Interior Minister Nicolas Sarkozy.

''I would have liked there to be fewer candidates and even for the party to rally around the First Secretary or the man or woman who could have got a general accord,'' said Mr Hollande, who lives with Royal.

Opinion polls show Royal is not only the clear favourite on the left, but also the only opponent capable of beating the tough-talking law and order advocate Sarkozy.

But she has upset some party members by questioning the Socialist's touchstone 35-hour work week and with her own hardline proposals to cut youth crime.

Some rivals say she lacks clear ideas and owes her high opinion poll ratings to her media-friendly image and good looks.

REUTERS SHB KN1503