DID SOMEBODY FORGET to tell Marion Barry that there's still one more election to go before he can assume office? Or is it that nobody can find him to let him know? True, his opponents -- Republican E. Brooke Lee, independent Dennis S. Sobin and Socialist Workers Party candidate Glenn B. White -- aren't exactly odds-on favorites to wrest the top job from a Democrat in this town. But shouldn't voters get at least one peek at the full field in debate before doing what they're going to do on Tuesday?

The excuse, of course, is that the incumbent is too busy doing his job to take time off for these campaign rites. Mr. Barry the Mayor, unlike Mr. Barry the Candidate, has been cranking out releases and announcements and appearing here and there for people to see. But what if all his supporters turned out to be too busy doing their jobs, or whatever, to vote for him next Tuesday?

Maybe we're old-fashioned in thinking that a healthy back-and-forth is a good thing, no matter how lopsided the contest may seem. It is a question of what might be called civic courtesy, showing a certain respect not just to the other candidates but to the public, which has a right to hear the issues fully aired. There is still time to stop playing coy -- but not much.