Come on back, Comeback Kid!! 

I'm sure some community theatres would hold your professional credential against you, but most would overlook that flaw in your background. 

Seriously, community theatre isn't about resumes, its about participation!  The only way to prove anything to anyone is going to be by what you do -- not a listing of what you did.  When I was directing, resumes were not nearly as important as what I was seeing at the audition in front of me.

Think about it, a lot of community theatre folks started with no training, no experience, no nothing but getting up enough nerve to show up at an audition.  So you haven't done anything in 20 years.  So?  Where've you been?  Time to get back in the saddle and have some fun.

I don't know what kind of community theatre you've got in your parts, but in my experience with most community theatres, if you worked professionally, you are in for a very pleasant surprise!  The atmosphere in community theatre tends to be very different (if it's not, find another one!).  It's about having fun. Doesn't mean that you won't work hard, but you should understand that in community theatre, high levels of artistic achievement happen more often than the stereotypes might lead you to believe and it's done despite all the distractions of life.  Having worked professionally, I found community theatre to be incredibly refreshing.  In some ways, I even found it more challenging! 

Go audition. If you don't get cast, help out with the show anyhow.  Do some tech work or stage manage or anything to get involved.  Get to know people at your community theatre and let them get to know you.  It's not always about talent.  I happen to have a very strong belief that in community theatre, the greatest benefits accrue to those who are most involved.  So, as a director, all other things being equal, I'm going to cast the person I know.  So go hang out and get known. 

If you do get cast, the process is pretty much the same as it always was:  Learn your lines and don't bump into the furniture. 

Keep us posted on how you do!

Since your fear seems to be that you won't live up to the expectations engendered by your resume, I suggest you try to get to auditions a little early, and when you hand in your audition sheet or resume, tell the director that you haven't been on stage for years and that you're very nervous about auditioning again. If you like, you could also ask if you could watch the auditions for a bit before getting up to read -- most directors are quite sympathetic and will be happy to do this, especially for a newcomer, but if turnout is small or if for some reason the director needs to do it differently, it may not be possible. It never hurts to ask, though. You may actually be much better than you think you are, and watching others audition might ease some of your apprehension.

Originally posted by Chris Polo (Crew are another matter -- they have a mandate from God to gripe about everything.)

Maybe go for the middle ground- say you have some professional experience from eons ago, and you're pretty rusty, be self-deprecating about it but provide details if probed.  I think that balances against the contradictory instincts of "I won't give him a chance because this has-been is so full of himself to tell me what he did half his life ago" and "I won't give him a chance because he didn't write anything on his resume and is probably too old to be learning a new trick."