There are, of course, a ton of steakhouses around downtown. I would be shocked if any one of them could not accomodate a large party.
Just to throw in a dark horse to consider, on the other side of town (i.e., West End) is a newish restaurant called the Blue Duck Tavern that specializes in ingredient-focused American. I should say ingredient-obsessed: it's one of those places that sources and notes every single farm or producer and builds its menu (not to mention philosohy) around artisanal qualities. This is not a place for aesthetics: they do very little plating, usually just serving protein in the dish it was cooked in; everything is a la carte, and they recommend you order starches and/or vegetables on the side. it can be a bit of free-for-all with everything spread out on the table as such.
The food, however, can be pretty glorious. They do an excellent job with meat, particularly less 'sexy' cuts: the marrow bone appetizer is heavenly; the short ribs fantastic; and the rabbit should not be overlooked. Their sides are well worth it: great wood roasted vegetables and fries cooked in duck fat. Fantastic applie pie for dessert.
Anyway, to get your concern, I was there with a party of eight; the room is rather cavernous, and I believe there are separate banquet rooms. The Metro stop (Foggy Bottom) is about 3.5 blocks south of the restaurant, but it's a nice walk.
24 & M Streets, Northwest, Washington, D.C.
{202} 419 6755