Since France is a member of the Council of Europe and follows the Bologna Process, this question could be very well be applicable to many other European countries as well.
The bottom line is that undergraduate studies in the US are basically thought out as a four-year program, not three years. France -as most Bologna participant states- has chosen the three-year option for the first stage of university studies, in this case the License. This is a bit different from Spain and the UK, where there is perhaps more tradition of working respectively with Latin American and US universities. Recognition of Licence and undergraduate studies in either direction is not immediate in other cases.
However, there are perhaps larger possibilities for American universities to exercise their own judgement and flexibility as to recognizing foreign titles, than in some European countries. So, in some cases it may be possible for an American university to say: "OK, I recognize your French degree as 3 years studies, now you need to pass this, this and that courses to enroll in graduate studies."
There is a good article on the subject here , that basically states that American universities are aware of the problem and are increasingly open to finding solutions for European students.
I would go straight to the Admissions people at your university of choice, find out how they see your precise situation and what advice they can give you.