WASHINGTON — The Obama administration soon plans to issue new guidelines aimed at giving the hundreds of prisoners at an American detention center in Afghanistan significantly more ability to challenge their custody, Pentagon officials and detainee advocates say.

The new Pentagon guidelines would assign a United States military official to each of the roughly 600 detainees at the American-run prison at the Bagram Air Base north of Kabul. These officials would not be lawyers but could for the first time gather witnesses and evidence, including classified material, on behalf of the detainee