Sarkozy handed over to Francois Baroin, minister for France's overseas territories, at a ceremony at the interior ministry.


Jacques Chirac, the French president, has given Sarkozy his backing as he is their party's designated candidate, but the two have been bitter rivals since Sarkozy backed a former Chirac ally for president in 1995.


Mixed results  


Sarkozy defended his record on cutting crime despite accusations that he has achieved only mixed results.


He criticised those who called for him to leave earlier or warned him against returning to the ministry just under two years ago.


"To some, I shouldn't have come back. They evidently didn't realise what the notion of duty is," he said.


"To others, I should have left sooner. They evidently didn't realise what the notion of a team is - you don't abandon your team when it's ahead in the fight against delinquency."


Polls show Sarkozy leads his socialist rival Segolene Royal and suggest he would win if they faced each other in the second round on May 6.


Polls published last week, however, showed his lead over Royal was slipping.


Surveys have also shown that if centrist Francois Bayrou could make it to the second round, he would win the presidency.


That remains a distant prospect, however, as only the two candidates with the most votes on April 22 go through to the run-off and polls show he is well behind Royal.