cjh (12/27/82)
In context, it is made very clear that "Klaatu barada nikto" means something like "Klaatu commands [that] [you] wait/do nothing/don't harm anything" (look again at the scene where Neal gets these words from Klaatu, who is specifically worried that Gort will go on a rampage).
bstempleton (12/31/82)
Actually, the phrase probably doesn't mean Klaatu "commands" anything. If you recall, it is Gort who is the boss. Old K is just around to communicate with the humans. The message probably means that he is hurt and needs help, and SUGGESTS he not destroy the world.