When I first came back from Europe, I was talking with a New York City tug boat captain, and he told me with my European titles, I could work as a captain if I was going from the US into international waters, but if I wanted to captain boats within US territorial waters, I'd have to get a US Coast Guard license. Granted, I never went that route, so I don't know first hand if you can get an equivalence - but from other things like this I've done, I would doubt it. They may accept parts of your current license and give you some sort of credit, but you'll likely have to do at least some additional work/pass an exam/whatever to get the USCG license. that may also depend upon how well documented you have your sailing experience.
The need to have a USCG license will also depend upon where you wish to do your sailing. Strictly US waters or across borders into other countries.
Best of luck to you. Where did you get your French license? Just curious.
dj