SANTA FE, N.M. — U.S. immigration and military authorities disclosed Monday that immigrants from 27 countries were being held at Guantanamo Bay Naval Station in Cuba, while revealing new details of conditions of confinement and defending the government's authority to transfer and hold immigrants at the military base. Court filings on behalf of the Homeland Security and Defense departments indicated that 40 immigrants with final deportation orders were being held at Guantanamo Bay as of Friday —