Jaap de Hoop Scheffer, Nato's secretary-general, spoke to politicians in France's lower house of parliament on Thursday, in an effort to back an attempt by Nicolas Sarkozy, the French president, to become a full member of the alliance.
Scheffer was scheduled to meet Sarkozy later in the day.
Greater role
Sarkozy is expected to formally announce a greater role for France in Nato in coming weeks, a move the country's leaders have traditionally rejected.
Scheffer said he "cannot say which posts France would hold", but insisted they would be "very important".
"By making these gestures, France has lost no sovereignty, and would equally not stand to lose if tomorrow she decided to take her full place within the alliance," he said.
France currently remains outside Nato's nuclear group and planning committee.
Sarkozy says new threats such as "terrorism" mean it is in France's interest to seek greater international co-operation and rejoin Nato.
Under pressure
Sarkozy's move came after Nato's chief and Barack Obama, the US president, urged European allies to send more troops to Afghanistan, where violence is escalating.
But there is opposition to rejoining Nato in France, with critics saying they do not want to forfeit France's ability to make its own military decisions.
Estelle Yousouffa, Al Jazeera's correspondent in Paris, said Sarkozy, facing falling popularity in opinion polls, could find it "a very hard task" to convince the public and politicians to approve his decision.
Charles de Gaulle, the former French president, withdrew the country from Nato's military command in 1966 in an effort to reassert France's independence after World War II.