According to an article posted on the official USSF website, FIFA will select 85 referees, assistant referees and video assistant referees for the 64 matches of the World Cup 2018 in Russia.
36 referees attended a FIFA preparatory seminar in Abu Dhabi (UAE), from 25-29 November 2017. They participated in a series of activities that included practical, theoretical and physical elements, including training sessions with local players.
Source: USSF
