The demonstrators were arrested at about 2:30 p.m., Park Police spokesman Sgt. David Schlosser said. The group included a number of military veterans, protesters said.
The policy that prohibits gays and lesbians from serving openly in the military is being challenged in federal court.
President Barack Obama has pledged to push lawmakers to repeal the law in the lame-duck session before a new Congress is sworn in. But administration lawyers have in the meantime defended "don't ask, don't tell" in court.