If you have acting credits in other countries (such as your home country) and a temporary job offer in the U.S., then you can apply for an O-1 Visa, which is the U.S. work visa for individuals that can demonstrate an “extraordinary ability in the sciences, arts, education, business, or athletics which has been demonstrated by sustained national or international acclaim and who are coming temporarily to the U.S. to continue work in the area of extraordinary ability.” The O-1 Visa is one of the most popular visas for actors and other performers that want to work in the U.S.
For more info, see: http://en.wikipedia.org/wiki/O-1_visa and the excellent Artists from Abroad website, which calls itself “The Complete Guide to Immigration & Tax Requirements for Foreign Guest Artists.” You might also want to check out the visa-consultant and legal services at sites like http://www.hooyou.com/o-1/faq.html and http://www.actorsevolution.com/visa.php. And visit the U.S. Citizenship and Immigration Services (USCIS) website for a list of additional visas.
Alternately, you could become a student at an acting school in the U.S., and use a student visa or J-1 Exchange Visitor Visa to enter the country.