France, Germany, Italy, Spain, Poland and Britain agreed to take the lead in forming the spearhead force, which would be available to deploy within a week in a crisis, Stoltenberg told a press conference after talks in Brussels.
"We have decided on the immediate establishment of the first six multinational command and control units in Bulgaria, Estonia, Latvia, Lithuania, Poland and Romania," he said.
"If a crisis arises, they will ensure that national and NATO forces from across the alliance are able to act as one from the start," the NATO chief said.
The string of bases will effectively coordinate the deployment of the spearhead force to the region in the event of a crisis.
Stoltenberg made clear throughout the day that the collective defence posture was in response to what he called Russian military aggression in Ukraine, which has unnerved NATO's eastern members.
It is also designed to counter any eventual threat from Islamist militants in Iraq and Syria as well as North Africa.
"We decided that this very high readiness force will consist of a land brigade of around 5,000 troops," he said, adding they will be supported by air, sea and special forces.
The spearhead force will be backed up by two more brigades in order to keep reinforcements coming in a crisis.
All told, the NATO response force will be increased to 30,000 troops from the current number of 13,000.
