Depends if you plan to fly by yourself (not with a US instructor). If you plan to do your own thing-- see below:
When you get to the United States, go to the nearest Flight Standards District Office (FSDO)-- look in the blue pages for U.S. Government-- Federal Aviation Administration.
Bring your valid license, medical and logbook from your home country. They will have you fill out an application form (Form 8710) and issue you a certificate based on your foreign license for private privledges for VFR flying. You have to apply for this in person-- it cannot be done by mail. With this you just get a checkout and possibly a flight review at any school or renting place and off you go. The certificate is good for life. Make sure that you always keep your foreign license and medical valid-- as the US certificate only "validates" your foreign qualifications.
The US is one of the easiest countries to get set up to fly recreationally.
Have fun.
PJ