Just as people begin to hum "Deck the halls with boughs of holly," while wondering where they could possibly have stored the Christmas tree ornaments, the urge comes upon them -- the urge to have a party, inviting all the people they haven't seen since last Dec. 15. There are among us sensible people who respond by immersing themselves in a hot tub until the craziness passes, but the rest of us go right ahead.

Maybe the best way to handle holiday entertaining is to invite friends to help you with the things you have to do anyway. For instance, take everyone out to the country for a winter picnic at a cut-your-own-Christmas-tree farm. Pile up wooly blankets to sit on, round up all the Thermoses you can find and fill them with hot soups, hot mulled wine or hot cider and rum. Pack ham biscuits, which are easy to eat with mittens on, and bring walnuts, apples and cookies for dessert.

To find out where to cut your own tree, send a post card with your name and address, and a request for a list of Christmas tree farms to the Maryland Department of Agriculture, Division of Marketing, Parole Plaza Office Building, Annapolis, Md. 21401. For Virginia, send a stamped, self-addressed envelope to the Fairfax Extension Office, 3945 Chain Bridge Road, Fairfax, Va. 20030. When you've chosen your farm, check to see if you need to bring an ax.

Once you've gotten your tree, you still have to trim it -- another occasion to turn holiday entertaining to a useful purpose. Lots of strong hands to steady the trunk, lots of opinions on how straight the tree is and which side shows to the best advantage, lots of hands to string the lights, unpack the ornaments, place a brilliantly colored glass ball precisely here and a silly yarn Santa Claus there. Serve your tree trimmers sandwiches, food they can get down and momentarily forget about while unraveling a length of tinsel or searching for a hook.

If you haven't already poured all your money into Christmas presents, the sandwiches can be elegant, open-faced affairs: smoked salmon on brown bread and butter with a small topping of horseradish and chopped egg; little dollops of caviar on crackers; a creamy liver pate smeared on crisp bread and topped with hot mustard. Add a couple of good bottles of wine, put Christmas music on the phonograph and the tree will be trimmed before you know it.

When the tree is chopped and trimmed, there is nothing left to do but invite anyone you still haven't seen to a caroling party. Check drug stores and book shops for books of Christmas carols -- buy one and Xerox the words to the songs; everyone knows the tunes. Tour your neighborhood, ringing bells and serenading folks until you've sung your way around a block or two. Then bring your carolers back to sit under the lights of the tree, drinking eggnog and eating the sweet rewards of the season -- Christmas cookies, Buche de Noel, mince pie, plum pudding and rich and chewy loaves of fruit cake.