I have a criminal background for Disseminating matter(s) harmful to juveniles, and I plead no contest for appeal purposes and was found guilty by the judge. A rabbi at my synagogue sent a letter to my Judge after being found guilty but before sentencing, essentially asking for leniency and sentencing. Now, I got probation, and it's been close to 2 years of my 5 year probation sentence, anyway, another rabbi, or senior rabbi sent a letter to every member of the synagogue, to every synagogue leader in the area outlining my criminal past and forbidding me to attend services anymore. I was equally turned away from another synagogue because of this letter. Is this defamation of character? Also in a letter they sent me they were giving me 30 days to reply but sent this letter out after only 4 days, so my reply really would have meant nothing considering they didn't even wait to find out that a rabbi (who left us 5 months ago) gave me a recommendation. Your advice is greatly appreciated. I live in Ohio, USA.

You submitted this question in a law section, so I won't attempt to address the issues of whether the rabbi's treatment is fair, or how to get back into the congregation, but just your legal question regarding defamation of character. If what the rabbi wrote in the letter about your plea and probation is true you have no basis for a suit, especially since these are matters of public record. Defamation of character requires the intentional dissemenation of false statements that harm your reputation. He can opine about how he views the facts of the case, and his decision to expel you and to recommend that others bar you as well. But if he characterizes you in a way that is knowlingly false - such as stating you've committed previous crimes when in fact he knows you haven't, then you may have a case.

ebaines is right I don't see any defamation. However, it is possible your civil rights are being violated.

Were you required to register as a sex offender? It may be that your right to worship is being interfered with. Its probably a longshot, but I would talk to the ACLU about whether you can sue for being blacklisted.

Your only hope and it is a slim one is to try and go over the senior rabbi's head, to a more senior rabbi. I believe the synagogue has the right to determine who attends. All they have done is set forth who can attend and who can't, and they gave an explanation (which apparently was factual) as to why.
Best guess is that one or more fellow worshippers complained.
The first rabbi's letter on your behalf has no bearing on the present issue.