Daalder said the mobile nature of the missile defense system gives NATO the ability to protect different countries across the alliance.

“We have looked at rules of engagement and a defense design for a wide variety of places that could be protected by the fact that the ship could be moved,” he said, adding that the system would “operate under NATO rules of engagement, NATO agreements on how the command and control system is supposed to operate, and formally under the operational control of a NATO commander, as opposed to a U.S. commander.”

Daalder said the interim NATO missile shield will evolve to an initial operational capability by 2015, at which point the alliance plans to field land-based Aegis SM-3 interceptors in Romania followed by additional interceptors in Poland by 2018. But that would leave little time for allies to grapple with the issue of political control over military actions taken in response to an attack.

“Given the short flight times of ballistic missiles, the [NATO] Council agrees [to] the pre-arranged command and control rules and procedures including to take into account the consequences of intercept compatible with coverage and protection requirements,” the alliance said in a declaration issued during the summit.

But there are still areas of tension as NATO tries build up its missile defense capability. Newly elected French President Francois Hollande acknowledged the logistical difficulty of having to make a political decision in the short time between the launch of a threatening missile and the time needed to pull the trigger. Command and control authority should not lie solely with the U.S., he said.

“There obviously needs to be a decision-making authority, and it is to establish this procedure that we want it clearly understood [by NATO] that this will be done in partnership,” Hollande said during a May 21 news conference in Chicago following the summit. “In this context [it] will not be solely the United States that makes the decisions.”

Hollande said NATO has made enough progress to allow France to support continued development of a missile defense shield, “with necessary vigilance.”

In the meantime, the declaration calls on the NATO Council to review implementation of the interim missile defense system and report on issues to be addressed in future developments by the alliance's next summit.

U.S. Deputy National Security Adviser Ben Rhodes said the partial defense capability reaffirms the Obama administration's commitment to missile defense in response to its assessment of the ballistic missile threat to the U.S. and its allies, which he says most likely stems from the Middle East and Iran.

“What we've demonstrated as an administration is not just talk on missile defense but action,” Rhodes said. “We have concrete commitments and plans to move forward with the deployment of this system, with four countries already stepping forward to play their part in hosting part of the architecture.”