SAFEKEEPING by Gregory McDonald (Penzler: $15.95). Even though dear old Dad and Mum were nothing to write home about in the first place--that would be the Duke and Duchess of Pladroman--their being done in by a Nazi bomb wasn't the worst thing that could have happened to their 8-year-old heir, Robby Burnes. The worst thing that did happen to the orphan was to be sent by the duke's solicitors to the safety of New York City--and to the tender mercies of martini-swilling hack journalist Thadeus Lowry, a one-time acquaintance of the duke, which gives you some idea of his taste in friends. Author McDonald, better known for his Fletch novels, has turned his attention away from his hip, wise-cracking, contemporary newspaperman to the hip, wise-cracking Robby Burnes, an innocent abroad on the seamy underside of New York during World War II. Exploited by Lowry in the yellow New York Star as a poor, orphaned (but blueblooded) war waif, Robby is just as casually lost by his guardian and, in turn, is kidnaped by a family catching the scent of ransom money, witnesses a murder and is pursued by the murderer, ends up as a bagman for a wealthy Park Avenue family bribing their congressman and ultimately becomes one of Mrs. Clearwater's 12 wards in a Harlem tenement. Sorry, but there's no way in the world that this lippy, overachieving kid can be portrayed as threatened by the bush-league villains surrounding him--despite author Macdonald's good-natured huffing, puffing and cutesy-pie plot inventions.