At the still, not-quite hour of six a.m. I look out to see the morning paper sail over the porch bannister and slide, plastic-wrapped, to a spot squarely in front of the door. As on down the street wheels of the bicycle whirl. ''Perfect pitch!'' I remark, and follow the bike with my eyes. ''Our new paper boy?'' someone asks. And I say, '' . . . is a girl.''