If we don't change standards, it will be very, very difficult to have any numbers -- any real numbers come into the infantry," Kelly told reporters at the Pentagon.
But the deputy commandant of the Marine Corps, Gen. John "Jay" Paxton Jr., espoused a more optimistic view.
"I think the Marines who happen to be women, who are going into those units, are committed to live up to that standard and contribute to unit efficiency and unit success," Paxton said in an interview with the Marine Corps Times published Monday.
The US Army fielded its first female infantry officer in April.