WASHINGTON — Defense Secretary Ash Carter has ordered a six-month study aimed at formally ending one of the last gender- or sexuality-based barriers to military service, saying the Pentagon’s current regulations banning transgender individuals from serving in the military need to be examined.

“The Defense Department’s current regulations regarding transgender service members are outdated and are causing uncertainty that distracts commanders from our core missions,” Carter said in a statement released Monday. “At a time when our troops have learned from experience that the most important qualification for service members should be whether they’re able and willing to do their job, our officers and enlisted personnel are faced with certain rules that tell them the opposite.”

Carter said he is creating a working group that will review the policies and determine if lifting the ban would have any impact on the military’s ability to be ready for battle. But he said the group will begin with the presumption that transgender people should be able to serve openly “without adverse impact on military effectiveness and readiness, unless and except where objective, practical impediments are identified.”

The plan, which was first reported by The Associated Press, gives the services time to methodically work through the legal, medical and administrative issues and develop training to ease any transition, and senior leaders believed six months would be sufficient.

Carter asked his personnel undersecretary, Brad Carson, to lead the working group of senior military and civilian leaders to take an objective look at the issue, including the costs, and determine whether it would create any insurmountable problems that could derail the plan. The group would also develop uniform guidelines.