Sarkozy said Paris would "take a number of decisions" in the coming weeks, and would likely increase the number of military forces it has here to train the Afghan army and police.
He was speaking to journalists after talks with his Afghan counterpart, Hamid Karzai, in Kabul.
Sarkozy said the international community could not afford losing the war against terrorism in Afghanistan.
That is why, the French president said, Paris is committed to help with the emergence of a "legitimate, democratic and modern" Afghan state.
Sarkozy began his visit with talks with General Dan McNeill, the commander of the NATO-led International Security Assistance Force (ISAF). He was also due to meet some of the 1,300 French troops based in Afghanistan.
French Defense Minister Herve Morin and Foreign Minister Bernard Kouchner were accompanying Sarkozy.
In November, Sarkozy told the U.S. Congress that French soldiers would stay in Afghanistan "as long as needed" and that failure was "not an option."
Most of the French soldiers are stationed in relatively secure areas around Kabul. Some of them are in the southern province of Kandahar, where six French Mirage jets are based.
Washington and other NATO allies have repeatedly urged France to send its forces to the more dangerous southern and eastern areas.
But Sarkozy said today that Afghanistan's problems could not be solved just through military means, a likely reference to efforts to use reconstruction and reconciliation to persuade rebel fighters to lay down their arms.
Sarkozy also said Pakistan had to understand that it "must engage resolutely" in the fight against terrorism.
On December 21, U.S. Defense Secretary Robert Gates said Al-Qaeda had "re-established itself" in Pakistan's remote Afghan border and begun to focus on attacking the Pakistani government.
But the Pentagon chief said "we haven't seen any significant consequence of that in Afghanistan itself."
U.S. and coalition forces have faced increased Taliban violence in the past two years.
Officials say there are more foreign fighters involved, including some linked to the Al-Qaeda terrorist network.