His comments state the reality of so-called Arab allies.
Carter acknowledged a missing element in the campaign: a more assertive role by Sunni Arab allies from the Gulf in the effort against Islamic State, a Sunni extremist group.
He said the United States had spoken to Gulf Cooperation Council leaders at a Camp David summit in the spring about creating a "Sunni Arab combined force" to help in the fight.
"That has not materialized among them," Carter said.
He suggested Sunni forces might not need to occupy territory but instead work at "enabling local forces."
That's a strategy that the United States moved decisively toward in October, when it announced it would send dozens of special operations forces to Syria to coordinate with rebels.
The United States last week announced plans to deploy elite American military teams to Iraq to conduct raids against Islamic State there and in neighboring Syria.
Carter told the Senate hearing that he was in touch with coalition partners to ask them to contribute special operations forces, including from the Gulf. The United States also sought other capabilities, like strike and spy aircraft, weapons and munitions.
"I too wish that particularly the Sunni Arab nations of the Gulf would do more," Carter said.