The Marines could be the first military branch to request a waiver from the requirement that women be allowed to serve in all combat jobs.

The Navy, Army and Air Force are not expected to ask for exemptions from the plan to fully integrate the nation's military, slated to begin in January 2016. But the Marine Corps request would be the latest indication that, despite the historic graduation of two women from Army Ranger School this summer, traditional combat roles would not be fully open to females.

The Pentagon is grappling with a desire to nudge the branches toward egalitarianism amidst concerns from some leaders that full integration would lower military capabilities. The Marines wrote a study on the impact of integrating women, which found that all-male squads are more effective in combat and less likely to be injured than integrated groups.

No final decision has been made about what the Marines plan to ask for. Exemption requests must be submitted to the Navy, of which the Marine Corps is a branch, by October 1.

READ: Two women make Army Ranger history

Navy Secretary Ray Mabus has said he does not want to prevent women from any type of military service. Defense Secretary Ashton Carter, however, will make the final decision about which jobs will be opened to women.

"I'm not going to ask for an exemption for the Marines," Mabus said Monday in Cleveland. "It's not going to make them any less fighting effective. In fact, I think they will be a stronger force, because a more diverse force is a stronger force. And it will not make them any less lethal."

A spokesman for Marine Corps Gen. Joseph Dunford said he met with Mabus on Thursday but declined to comment on Dunford's recommendation, though he did confirm a suggestion had been made. Nevertheless, Marine Corps officials on Friday began to defend their apparent decision, with one noting that 94% of the 335 primary military occupations in the Corps are currently open to women.

The exceptions are the latest episode in the simmering tensions between Mabus and critics of the military's march toward more integration. On Thursday, Republican California Rep. Duncan Hunter of the House Armed Services Committee called for Mabus to resign.