Dear Pussycat: Some of us find it easier to say in a letter whatever it is we want to express--love, rage, outrage, affection, resentment, enthusiasm, a request to do a chore-than we do person to person or even phone to phone. I've been writing letters, some- what successfully I think, since I was-eight-years old. I got President Franklin Roosevelt to write to my wheelchair-bound (from polio) sister by dropping him a line at the White House. Some of my letters don't quite make it, of course - trying to get The New York Times publisher Arthur Sulzberger to fire his vicious play reviewer Frank Rich who tore apart my husband's perfectly fine play, A Few Good Men. He wouldn't do it - no recourse but to write the reviewer himself, "Dear Frank, you bastard! etc." I've thanked designer Emilio Pucci for turning small bust and big hips into goddess stature with whammo fabric and genius engineering, and kept a few beloved employees from jumping ship or into the river with careful flattery. Wouldn't you like to see a little collection of my best, meanest, and happiest notes that reflect a pretty fascinating New York life, a career they don't make many like, love and friendship with buddles, and a few razzle-dazzle celebrities? If you like good old-fashioned staying-in-touch by correspondence, here they are!