The report noted that the Pentagon’s high- and medium-security lockups where the Guantánamo captives could be held were at 48 percent occupancy earlier this year.

The report also considered the use of federal prisons and included a map showing 98 lockups across the country that already house about 370 prisoners convicted of terrorism-related crimes. Those facilities, the report said, could be suitable to incarcerate the Guantánamo captives.

But it notes that, while federal prisons “have the correctional expertise to safely and securely house detainees with a nexus to terrorism,” the Bureau of Prisons and U.S. Marshals Service that moves prisoners “would need additional statutory authority to take custody of Guantánamo Bay detainees.”

Interestingly, the report said of the civilian terror-related convicts, only 41 were being held at the maximum-security prison at Florence, Colo., the so-called SuperMax best known for holding al Qaida convicts.

The report was also made public as about 100 U.S. officials involved in war-on-terror detainee policy were meeting at the U.S. Southern Command in Doral — notably the Pentagon’s deputy assistant secretary of defense for detainee affairs, retired Marine Col. William K. Lietzau and Navy Rear Adm. John W. Smith, the current commander of the detention center at Guantánamo.

Only U.S. military and civilian officials with “secret” security clearances were allowed to attend the meeting, according to participants. One known exception was a delegate of the International Committee of the Red Cross who made a presentation Monday. ICRC spokesman Simon Schorno would not provide details.

Participants refused to discuss the nature of the meeting, the composition or the topics discussed, said Army Col. Gregory Julian, Southcom’s spokesman. But a Defense Department official said on background that the possibility of Guantánamo’s closure was barely mentioned and the GAO report came up only briefly Thursday morning without in-depth discussion.

In Washington, Feinstein’s communications director, Brian Weiss said that the senator, who has long advocated for the closure of the detention center, asked for the report in 2008. She waited about two weeks to release the report — and her remarks on it — because it arrived the same week that retired Gen. David Petraeus was testifying about the attack on the U.S. diplomatic post in Benghazi, Libya, in his capacity as the recently resigned CIA director.

“She received it, she read it, she released it,” said Weiss, adding that the senator had not discussed it with the president.

The report was written by the GAO’s Homeland Security and Justice Team, which also provided a classified version that Weiss said went no further in saying whether or where to move the 166 Guantánamo detainees.