I’m not sure what wikipedia used as a source, the the National Park Service web site list 432 locations on their “Find a Park” page.
http://www.nps.gov/findapark/index.htm
I'm sure the libs will use the ~400 number to weasel out of obama's lie, but technically his statement is false. Saying "Hundreds of national parks would be forced to close..." is a lot scarier than saying "Hundreds of sites administered by the national park service would be forced to close...". obama knows that. He's intentionally bending the truth to spread fear.