but in order for you to get admitted into a JD program, you need to take LSAT in the first place...which is a torture; normally LLM program does not require LSAT.
如果在國內念了法學的研究生 -- yeah you can transfer some credits, but you may need to get your degree and transcript evaluated and certified by some American Education Institute, and in reality, if tuition is not really a big problem, I highly recommend you to take as many courses as you can -- you are going to learn a lot.
Law school mythology -- first year is scared to death; second year -- busy to death; third year -- bored to death... so, be prepared. good luck.