Happy endings are hard-earned in Owen Parry's ''American Christmas Stories,'' and gifts don't come in tidily wrapped packages. If you're really lucky, you'll be rewarded with a lump of coal. That's what one secret Santa (a bighearted, small-town Pennsylvania cop) delivers to freezing, out-of-work miners in the 1887-set ''Coal & Iron.'' In ''The Christmas Joe,'' a Depression era waitress gets a baby and the Virgin Mary she ain't. Parry has an almost Dickensian eye for detail, and a light hand with religious themes. Also in Strike the Harp!, irreverently playful poems tweaking the three kings, holiday shopping, and more punctuate each short story.