WASHINGTON — American and NATO military planners, facing continued political uncertainty about whether foreign troops will remain in Afghanistan after December, have drawn up plans to deploy a force this summer that is tailored to assume a training mission in 2015 but is also small enough to withdraw if no deal for an enduring presence is reached, alliance officials said.

With President Hamid Karzai of Afghanistan refusing to sign security agreements approving a presence for American and NATO troops after 2014, allied military planners have been forced to prepare for both sudden success and abject failure of proposals for a continuing mission to train, advise and assist Afghan forces after combat operations officially end this year.

The decision on whether to extend the foreign military presence is a political one, and it will be decided first by Mr. Karzai and then by President Obama and the elected leaders from NATO nations. The process has brought vitriol in Kabul, the Afghan capital, and deep concern in Washington and allied capitals.

The delays have complicated military planning, since the governments of nations that contribute troops must approve any sustained deployments — and the required financing — months in advance, with a number of notional deadlines for finishing an agreement already long passed.