It's being twenty plus years since I did it so it may have changed.I belive you will have to get a private or commercial license first.Not a licence validation based on your foreign licence but an actual private / commercial then the faa instrument written exam and a flight test.I sure someone on here will have more up to date info.You could also contact one of the many EASA/FAA schools in the US and I'm sure they will tell you exactly what is required.