I find it implausible that Geary was participating in a perjury trap. At the end, he remains exactly as vulnerable to blackmail as he was going in, and even if Michael were immediately jailed, he doesn't want to give a vengeance motive to people like Hagen and Neri.

Geary references his "own committee." I think that Geary is not a member of the gambling committee, but is sitting in under the cover of the special interest a Nevada senator has in the links between legal and illegal gambling. I don't think a senator who was assigned to the committee, with it's attendant publicity, would give priority to a hearing on any other matter at that time. I think that Geary sat in just long enough to introduce the notion that the committee was an example of anti-Italian prejudice, then left because his usefulness to the Corleones was at an end, with his own committee as an excuse that he himself had scheduled.