WASHINGTON (Reuters) - Republican senators called on Wednesday for the rights of foreign terrorism suspects at Guantanamo Bay prison to be legally defined even as the Bush administration said the inmates could be jailed there "in perpetuity." ADVERTISEMENT The prison, currently holding roughly 520 inmates, opened on the U.S. naval base at Guantanamo Bay, Cuba, in January 2002 in the aftermath of the Sept. 11, 2001 attacks on the United States. Many of the detainees have been held for more than three years, and only four have been charged. At a U.S. Senate Judiciary Committee hearing, Republican Chairman Arlen Specter...