The French and British leaders were talking after a conference in Paris between envoys from 60 countries dubbed "friends of Libya" and the leaders of Libya's new rebel interim regime, the National Transitional Council.
"Qaddafi must be arrested and the Libyans will decide if he must be tried in Libya or before international justice," President Sarkozy said, in comments immediately echoed by the British prime minister.
Qaddafi and his son Seif Al-Islam have been indicted by the International Criminal Court in The Hague on suspicion of having committed crimes against humanity by ordering mass killings during their crackdown on a revolt.
But, now that the rebellion has driven the pair from Tripoli and begun to form its own government, some in the NTC have suggested that Qaddafi should be tried at home if and when rebel forces track him down.
For his part, the ousted strongman has continued to issue defiant audio statements through a Syrian television channel vowing to fight to the death.