Less than one-quarter of the U.S. military’s Iraq and Afghanistan war veterans who show signs of post-traumatic stress are referred for additional mental health treatment or evaluation, a government study finds.

The report released Thursday said about 5 percent of the veterans interviewed after they returned from combat tours appeared at risk for post-traumatic stress disorder. Of those, about 22 percent are referred for more health care.

The Government Accountability Office said the Defense Department cannot guarantee that those who need referrals get them, and there appear to be inconsistencies in how health care workers from the different military services determine who needs a referral.

The investigative arm of Congress found that 9,145 of the 178,664 service members reviewed may have been at risk of combat stress. Also, 2,029 were referred for additional help.

Dr. William Winkenwerder Jr., the assistant secretary of defense for health affairs, disagreed with suggestions that not all veterans who need referrals get them. In a response included in the report, the Pentagon said the clinicians are familiar with combat demands and, in some cases, a medical referral or treatment may prolong symptoms that could disappear naturally.

In a conference call with reporters, Winkenwerder issued a strong defense of the department’s programs, which he said are the best the Pentagon has ever offered to returning veterans. He added that there is no correct number of people who should or should not be referred for additional treatment.

Medical experts, said Winkenwerder, can make any number of recommendations, including suggestions that a service member talk to a chaplain or his own medical doctor.

He added that, according to Defense Department surveys, 80 percent of the service members said they were very happy with the services and support provided in the post-deployment screenings.

Combat stress symptoms may be relieved by rest and a return to normal daily life, the Defense Department said.

Pentagon spokesman Bryan Whitman said the military is making more services available than before for troops returning from war. He said there is less of a stigma for those who decide to seek help and more understanding about the stresses of combat.

The report recommended that the Pentagon determine exactly how health care providers are deciding who needs a referral, to explain why some military services are more likely than others to refer veterans who show signs of post-traumatic stress.

According to the report, the Army and Air Force referred 23 percent, the Navy referred 18 percent and the Marines referred 15 percent.

During the screening process, service members are asked four questions. If they answer yes to three or four of them, they may be referred for additional mental health evaluation, although most are not.