The Pentagon has been using a little-known power to obtain banking and credit records of hundreds of Americans and others suspected of terrorism or espionage inside the United States, part of an aggressive expansion by the military into domestic intelligence gathering. The C.I.A. has also been issuing what are known as national security letters to gain access to financial records from American companies, though it has done so only rarely, intelligence officials say. Banks, credit card companies and other financial institutions receiving the letters usually have turned over documents voluntarily, allowing investigators to examine the financial assets and transactions of American military personnel and civilians, officials say. Full Story