Closed at the time of writing to the public. I was so disappointed, as this was one of the places I *really* wanted to go to in LA, having seen the buildings in so many films. Cunningly, the authorities had hidden most of the signs to the observatory (or painted them temporarily out) in order to discourage visitors. We were only able to get to within about 200 metres of the place :-(
The Wikipedia page for the observatory contains more information.