Who’s the most powerful actress in Hollywood? Julia Roberts, named yesterday to the Hollywood Reporter’s annual list of the entertainment industry’s most influential women. The “Erin Brockovich” star, 33, who commands $20 million per picture, already makes her the highest paid actress in Tinsel Town, came in at No. 3 on the list. (No. 1 is Paramount Pictures chief Sherry Lansing.) “Julia Roberts is really the only actress in Hollywood who has the ability to have any project she’s interested in made,” said Christy Grosz, managing editor of special issues. P.S.: Even though her “Harry Potter” has yet to make it to the silver screen, author J.K. Rowling came in at No. 50 on the Reporter’s list.