Thanks for all those suggestions. I went through all of them but they all already do say 12-hour time in the relevant entries. I still don't see an option in the GUI gnome clock preferences to change to 12-hour time, which is sort of making me think the clock or the panel or something has a different idea of what my locale is and so it's defaulting to what it thinks my region uses? But that's just a wild guess in the dark and I can't see anything in gnome configuration editor that seems even vaguely relevant to that.
PS Thanks for the tip about the distro thing, as you can now see it's opensuse 11.3
sorry for not stating that in advance.