Have you tried the setxkbmap command without any spaces inside? It should work but Russian letters won't be very suitable for typing setxkbmap us to switch the layouts back.
It is possible to choose a keyboard shortcut for this task. On Lupu (and hopefully on Precise): xkbconfigmanager - Options - Group Shift/Lock behavior.
Or you might find this gui program useful: fbxkb (a thread in this forum)