I raise an eyebrow at the claim of National Park Service estimates, since the NPS no longer gives estimates (it got tired of getting brow-beaten by Leftists for "underestimating" numbers at their various causes). However, it seems that the pro-war counter-demonstrators may have outnumbered the anti-war peace activists at this weekend's rally. See here and here (picture shamelessly pinched from Michelle Malkin's place, where there are tons more). WaTi coverage on numbers is vague, bears either side's reading. I read it to mean the numbers were about even.
The most telling thing is the photos of the crowds. Meet the anti-war protesters. Now meet the counter-protesters.