A DEMOCRATIC CONVENTION right here in this town? Why not? That's what Mayor Barry is seeking, and we're all for it. The obvious naysayers--the mayor's political critics, other Democrats who see more votes or less humidity somewhere else, and Washington correspondents with wanderlust--will no doubt cite reasons for not holding the party at home. But the capital of the country is a natural, not to mention an excellent spot for families seeking some diversion from caucuses, platforms and speechifying.

There is also the not-so-slight matter of a brand- new Convention Center--where four exhibition halls, 40 meeting rooms and more than 800,000 square feet of useful public space should fill the party bill. This kind of event, after all, is what the center was built for and, for that matter, what the city was built for in the first place. Besides, with so many Democratic presidential hopefuls from so many different regions, Washington becomes a perfect neutral DMZ (Democratic Majority Zone).

The big catch, of course, is that candidates may find it awkward to do the old anti-Washington campaign bit while they are all guests here and while all the delegates are getting a closeup that shows dedicated federal employees who have more on their minds than living off the fat of someone else's paycheck.

Already, Washington's bid application is being prepared for submission this week, and a formal presentation to the party's site selection committee will be made in mid-February, with a decision scheduled for April 8. No one yet has picked an alleged "front-runner" in this contest, and nobody has to wander around New Hampshire or into the family rooms of Iowa on behalf of a candidate-city. It may be a long shot, then, but we're pulling for Washington on the first ballot.