Last week's release of long-secret Justice Department interrogation memorandums has given rise to starkly opposing narratives about what, if anything, was gained by the C.I.A.'s use of waterboarding, wall-slamming and other physical pressure to shock and intimidate Qaeda operatives. Senior Bush administration officials, led by Vice President Dick Cheney and cheered by many Congressional Republicans, are fighting a rear-guard action in defense of their record. Only by using the harshest methods, they insist, did the intelligence agency get the information it needed to round up Qaeda killers and save thousands of American lives.