By Jon Boyle

PARIS, Feb 23 (Reuters) French President Jacques Chirac rewarded leading loyalist Jean-Louis Debre with the top job at the Constitutional Council today, in what could be one of the last major appointments of his 12 years in power.

In his new role, Debre will be guardian-in-chief of France's constitution, a text largely written by his father Michel with post-war leader General Charles de Gaulle in mind.

The body's nine members -- former presidents may also sit on the body in addition -- rule on electoral disputes and vet all new laws passed by parliament. They serve fixed nine-year terms.

Presidents past have also named loyalists to the post, a move that could complicate life for an incoming administration of a different political shade.

Chirac is widely expected to announce next week whether he will seek a third term or retire in May.

The late president Francois Mitterrand named his close ally Robert Badinter to the post in February 1986 as his Socialists appeared set for a heavy election defeat, a move he repeated in 1995 with former foreign minister Roland Dumas.

As speaker of the lower house of parliament Debre, an investigating magistrate by profession, won over deputies from all sides with his pugnacious, witty and even-handed chairing of the National Assembly's frequently rowdy sessions.

But his traditional conservative roots made Debre a visceral opponent of the free-market economic leanings of Interior Minister Nicolas Sarkozy, the frontrunner to replace Chirac in the presidential elections.

Debre opposed Sarkozy's calls for constitutional change, defended judges against Sarkozy's charges of being soft on repeat offenders, and criticised the UMP's leader's pledge to make a clean break with the policies of the past 30 years.

But should Socialist Segolene Royal win the election, she is unlikely to have problems with Debre, who has spoken well of her in public. Royal's campaign manager Jean-Louis Bianco has said he would have no problem with Debre's appointment.

REUTERS SAM HT2357