Non-US citizens can become referees in the US, Luis. There are 3 main sets of rules in the US. NFHS, which governs our high schools (teenage boys and girls); NCAA, which governs our university teams; and the NBA. The high school rules are not available online, but here are the links for the other two:
NBA:
http://www.nba.com/analysis/rules_index.html
NCAA:
http://www.ncaa.org/library/rules/20...ball_rules.pdf
Good luck with your travels to the US.