I have dual citizenship (US and Russian). Currently I'm living in the US (Florida resident) and planning to move to Russia permanently. I know, that if I withdraw from 401K before retrirement age I will have to pay penalty (10%?) and federal and state taxes (something like 30%?) What if I withdraw form my 401K after I establish tax residence in Russia (start paying taxes in Russia)? Would I still have to pay federal and state taxes on the amount of 401K in the US when I withdraw?

Florida has NO state income tax, so no worries there! :-)

Yes, you would STILL have to pay the federal tax and the 10% Early Withdrawal Penalty! :-(