Secretary-General George Robertson told a news conference on Monday that the issue of a single command in Afghanistan had been talked about during a meeting of the 19-nation alliance's defence ministers.
Robertson played down any immediate plans. "We've not yet got to the detail of discussing how it might be carried out."
US Defence Secretary Donald Rumsfeld confirmed there was no timetable for a possible merger of Operation Enduring Freedom with NATO's International Security Assistance Force (ISAF).
But with so few troops, any possible transition in command may prove ineffective.
The most pressing issue for the ministers is how to plug embarrassing equipment gaps in the existing Kabul-based force, which only has three helicopters.
Such problems are ruining the credibility of alliance plans to extend ISAF's stabilising influence into other towns in Afghanistan where the Taliban are back on the offensive and a resurgent opium trade has sprung back to life.
Robertson, who has harangued allies for weeks to provide helicopters, said that without real commitment "Afghanistan and its problems will appear on all of our doorsteps".
French Defence Minister Michele Alliot-Marie said she had urged her counterparts to avoid trumpeting plans for military operations they were not able to carry out.
"I called for caution because when we announce something we must be sure we can do it," she told a news conference.
NATO has agreed to take responsibility for six Provincial Reconstruction Teams, groups of soldiers who carry out small development projects or provide security for aid workers.
But military planners say that to do this NATO would have to deploy up to 3000 additional soldiers and set up a forward operating base, perhaps in neighbouring Tajikistan or Kyrgyzstan, to provide these teams with protection.
"If this proves a success...NATO might take over military operations in Afghanistan sometime in the future, although that remains to be seen," Rumsfeld said, adding it was "some distance out".