Yes, Janet Auchincloss, Jackie's Mom, is snuggled at the Watergate after splitting from her mate of late, Bing Morris. But she's busily combing Georgetown for another house. (Remember she sold her manse at 31st and O when she wed Bing two years ago?) . . . Yes, that was Mick Jagger, slinking into Germaine's with a spicey spike-haired belle, answering to the name of Suzy. Down the Jagger hatch: champagne, chicken and shrimp in rice paper, steamed rockfish with ginger and scallions, and veggies with oyster sauce. These are the things our grandchildren will ask us, much later . . . Yes, that's our very own Carol Shapiro, ex of hotshot lawyer David and former chatelaine of Prospect House, who's to co-host a benefit with Gov. Hugh Carey and the fair Engie tonight. This one's for former Mondaleman Douglas R. Stevens. Doug's racing for the New York seat now sat upon by in-the-news John LeBoutillier. John, of course, is a Harvard man who has millionaire cousin Glo Vanderbilt on his side. Doug's a Harvard man whose benefit's at millionaire Stew Mott's house. It's so hard to choose, really. Wednesday: Something borrowed, something blue.