Hello. I am a prospective applicant from LL.M in USA next year and I would like to ask you about the english proficiency requirements. Based on the fact that I anticipated that my TOEFL score would not exceed the limit set by certain universities, especially Berkeley, do u know if it possible to submit the low TOEFl score before the deadline and then retake either the TOEFL exam in December of send them IELTS results? Would be that acceptable or my application would not be examined at all?

Thank you very much in advance.

You always have the possibility of updating your original TOEFL score. So as long as your application is under analysis you may send an updated score.
Generally, IELTS is not accepted in US Law Schools.

Berkeley is one of few US law schools accepting IELTS. If your TOEFL score less than 100 you can send them IELTS result instead. Of course it shall be 7 at least.