brazillian all you can eat bar-b-que
The place you're thinking of it Green Field Churrascaria, at 1801 Rockville Pike (just a bit south of Congressional Shopping Center, just a bit north of Montrose/Randolph Road). It's on the ground floor of an office building.
Schedule your birthday celebration at a busy dining time - rapid turnover equals freshly-grilled meats. We went there once at a quiet time, and the grilled and fried buffet items definitely suffered from lack of turnover.
If we go again, I'll probably stick with the duck and the sausage - the beef items tend to be cooked medium to medium-well. (I'd be more enthusiastic about the place if I could get the beef while it's still rare)