Politicians are nothing if not two-faced. That glowing speech could have been a two-faced speech, IMO. When he says "These hearings on the Mafia," who might he have meant by "Mafia," if not the witness in the chair? And when he says, "An' it'd be a shame, Mr. Chairman, for just a few rotten apples to spoil the whole bunch," who could he have been referring to by "bad apple" if not the witness in the chair?
I also think he was playing that two-faced game at Anthony's party. He knew that Michael was a gangster, and assumed that others at the party knew that Michael was a gangster--and that Geary knew it. So, he refers to Anthony as "Anthony VY-toe Cor-lee-ON," IMO deliberately mispronouncing the name so the thousands of people there would get the impression that he wasn't very close to the Corleones--just making another stop on the rubber-chicken circuit. Later, in private, he sharpens it up to "Mister Cor-lee-OWN-nee," and then makes with his hair-and-clothes critique.