The San Francisco Chronicle OCTOBER 5, 1990, FRIDAY, FINAL EDITION Sinead O'Connor kicks back. After Frank Sinatra said he'd like to boot the skinhead singer in the butt for prohibiting the playing of the national anthem at a recent concert, the Irish rocker snapped back on ''Entertainment Tonight,'' ''It's hilarious that Frank Sinatra of all people, considering his . . . rumored connections, should be in defense of America.'' She added, ''It's probably very important to Frank that the American authorities think he's on their side.'' When asked if O'Connor was referring to Sinatra's alleged ''connections'' to organized crime, her spokeswoman replied, ''I don't know; make of it what you will.'' Frank's flack said, ''Mr. Sinatra stands by his original comments.''