Prince stopped by Mio Gelato in Georgetown yesterday with five bodyguards to buy some ice cream, and was frustrated when the store couldn't give him change from his wad of $100 bills, so he had to borrow $5 from his driver . . . Rumors on H Street is changing its name. Starting Saturday it will be known as Mike Baker's, named for the person who once owned Baker Brown's . . . Track star Mary Decker, whose collision at the Olympic Games destroyed her hopes for a gold medal, will marry British discus thrower Richard Slaney on Jan. 1 . . . Olympic gold medalist swimmer Rowdy Gaines is in town promoting "Shooting for the Gold," a collection of Olympics photographs . . . Rock 'n' roll pioneer Little Richard's $115 million lawsuit against three record companies he says owed him royalties on his hit songs since 1955 was thrown out of U.S. District Court in Los Angeles . . . Maurice Daniels, a 27-year veteran of the Royal Shakespeare Company, will be director-in-residence for December at Catholic University's Hartke Theatre, where he will direct a modern version of "The Taming of the Shrew" . . . Probably to show that Vice President Bush wasn't the only one who could make derogatory comments about Democratic vice presidential candidate Geraldine Ferraro, President Reagan is quoted in People magazine as saying to Israeli Prime Minister Shimon Peres that Ferraro had helped his campaign. "I received enormous backing from a male organization for my reelection. Indeed, the Organization of Men Married to Italian Women" . . .