There is nothing novel about a live Christmas tree if it's an evergreen. But a live walking tree is another matter.

"The Living Christmas Tree" was the original name for a holiday "tree" designed to be worn by a young lady attending a Christmas party around the turn of the century. Adelia Beard included the idea in her book, "Things Worth Doing and How to Do Them," which she wrote in 1906.

A life-size mannequin models the Christmas tree cape taken from this turn-of-the-century idea in the Smithsonian Institution's "Trees of Christmas Exhibit," in the Museum of American History (formerly the Museum of History and Technology) from Dec. 19 to Jan. 4. The idea can be worn as a Christmas party costume or adapted to make a nonmobile decoration.

To make your own "Living Christmas Tree," here is a simplication of the 1906 directions. The original had as its foundation a cloak made of green cambric with green tissue-paper fringe for a leafy effect. In the modern version green felt is used for the cape and for the fringe. Felt was chosen because it is strong, doesn't ravel, hangs well and may be glued as well as stitched. The pattern to be used for the cape is Butterick No. 3361, without a hood. Approximately eight yards of felt is needed for the cape, hat and fringe, using the medium-sized pattern for sizes 12 to 14.

Make the cape according to the pattern directions. Instead of turning up the hem in the normal manner, pin it over a Hula-hoop, then stitch it by hand. The hoop makes the hem stand out in a circle. Sew small bells around the bottom of the hem so the cape will make a tinkling noise as the young lady steps about the room.

Sew hooks and eyes on the front closing.

The hat is made of poster board covered with felt. Cut the cardboard in a triangle with the longest side the same as the model's head measurement plus one inch for the overlap, and 18 inches for the height. Roll the triangle to a cone shape and glue. Cut a piece of felt the same size and glue over the cardboard frame. Sobo glue is god since it doesn't stain the fabric. Place the hat on the model's head and measure the distance from the bottom of the hat to the shoulders of the cape. Cut a strip of felt to that measurement. Pin or glue that piece of felt to the bottom of the hat and then to the shoulders making a smooth line from the to of the hat to the bottom of the cape.

Before proceeding any further, cut a small hole in the top of the hat and insert a dowel to which a gold paper star has been attached.

The cape is ready for its "leaves" of fringe. Cut strips of felt five inches wide, fold them over and cut through the folded side leaving an uncut heading which will be stiched to the cape. Beginning at the bottom sew the fringe around the cape, allowing it to reach to the edge of the hem. Above the first row of fringe, and overlapping it, sew the second row. In this way put on row after row of fringe, always overlapping it until the cape is covered, then continue the fringe all the way to the peak of the hat. It seems easier to do this stitching by hand using large basting stitches, stopping, of course, at the front opening so the young lady can be helped into and out of the cape.

When all the fringe has been attached, it's time to decorate the "tree." Start with the garlands, in this case tinsel and strung popcorn. Make sure the tinsel is not the wide, modern variety, but if that is all you can find, trim it to make it narrower and more old-fashioned-looking. Paper chains may also be used. Stitch or pin the garlands in loops.

Decorate the tree in the Victorian manner using lightweight ornaments. Colorful Christmas balls may be used. Reproductions of old ones are on sale in many shops. Unwrapped toys, cookies, candy canes, cornucopias made of paper and fabric, paper fans, birds and flowers work. Avoid anything plastic.

Allow garlands and tinsel to hang free along the cape opening until the "Christmas Angel" is helped into the cape, then they may be pinned into place.

If you have neither an antique mannequin nor anyone who wants to be a walking Christmas tree, a proper foundation can be made by attaching a mannequin head, such as those used in store displays, to a wooden stepladder. a

The heads available have very long necks; this must be taken into consideration to keep the proportions correct. Nail a three-inch block of wood to the top rung of the ladder, then attach the head to that by wrapping the neck and the ladder with strong strapping tape. The ladder should be opened to give the needed support; place the Hula-Hoop on the floor to act as a guide. The support on the ladder for holding paint may be folded up out of the way.