It is important to note that you should never try to work as a model in the U.S. without the proper type of work visa, even if you are extremely famous. Your agency will have to apply for and obtain one of two types of model visas:
an O-1 visa, or
an H1-B visa
Both model visas are reserved for those individuals who have proven they have extraordinary ability or widespread acclaim in their professional field, and models are no different.