The two, Turkish-Americans Sinan Narin and Eyup Yildirim, are among 19 members of a security detail for Erdogan during a White House visit that have been indicted in the May 16 attack.
The 19 were identified from detailed video footage of the daylight assault on Kurdish and Armenian protesters outside the residence of Turkey's ambassador, following a meeting between Erdogan and President Donald Trump.
The protestors were beaten and kicked, with a number taken to the hospital for treatment of serious injuries.
In a brief court hearing today, a lawyer for the two said both pleaded not guilty to the charges.
Narin and Yildirim are the only two arrested in the case. The other 17, two Turkish Canadians and 15 Turkish citizens, including top Erdogan bodyguards, remain at large.
On September 1 Erdogan, who labelled the protestors "terrorists," blasted the US indictment of the 19, saying the case was a "scandalous demonstration of how American justice works.