Iraq's most influential Shiite cleric has been quietly issuing religious edicts declaring that armed resistance against U.S.-led foreign troops is permissible — a potentially significant shift by a key supporter of the Washington-backed government in Baghdad. The edicts, or fatwas, by Grand Ayatollah Ali al-Sistani suggest he seeks to sharpen his long-held opposition to American troops and counter the populist appeal of his main rivals, firebrand Shiite cleric Muqtada al-Sadr and his Mahdi Army militia.