Hot news. Patti Davis, the First Daughter, may tiptoe to town, on stage. Her Vehicle, as we say in show biz: a play called "Key Exchange." It's about an Amorous Triangle among people who ride bicycles. (What will the Moral Majority say?) Patti was a smash, reading for the role in San Diego. Producer Frank Gero -- Liza Minnelli's Pa-In-Law -- says they're on the verge of the Great Signing. Her part, darlings, was played in L.A. by fallen Angel Kate Jackson . . . And don't pigeonhole peppy Jack "Quincy" Klugman in his usual Gloomy Pursuits, too soon. Here comes his True Cause: He's to be chief sunshine-pusher for the Solar Lobby's hot and high-powered new TV campaign . . . Meanwhile Mary Crisp, rudely booted from her niche as co-chair of the dear old Republican National Committee at the dawn of the Reagan Era, is off to California to Speak to the natives, Ear hears. Her missionary topic: "Moral Imperialism: Are You Ready For It?" . . . Sons of the South battling the chilly weekends watching "Southern Gothic," the Capitol Hill Arts Workshop's haute Poetic Offering. Its most Gothic secret: the author's Hidden Lives. Hastings Wyman, in the closet, is publisher of savvy wee Southern Political Report, and, odder yet, speechwriter for the oilies at the American Petroleum Institute. Ear salutes Renaissance Man . . . And the Washington Press Club's big Congressional Dinner Jan. 27 will star Jim Brady, recovering Presidential Pressie. He's to be grandly handed a Key to the cliquish new Club House. The President Himself will roll in on celluloid. Ear hears he's busily filming his Grand Tribute to Jim. The split second the scribes sit down for dinner, the lights pop off and the Prez pops on-screen. Elbows out of the soup, darlings. And no scribbling on the napkins, this time. Back Friday.