Are you going to actually be staying in DC or in a nearby area (Virginia or Maryland)? If you're not actually staying in DC, you might be OK to take your handgun with you so long as it's legal to posses where you're actually staying (if not in DC) and you leave it there when traveling into DC.
Smith, and Wesson, and Me. -H. Callahan
Well waddaya know, one buwwet weft! -E. Fudd
All bad precedents begin as justifiable measures. -J. Caesar