A LADY OF considerable experience of life, having passed the three-score-and-10 mark, holds to the opinion that if anything terrible is going to happen (such as the dog dying or the radiator bursting or misplacing your wedding ring) it will happen in the week between her birthday and Christmas.

She is, of course, not the only to be afflicted at the end of December with accidie or weltschmerz , that indefinable sorrow for what never was or never will be. It is for solace in the solstice, depending upon where we are and what gods we put our faith in, that we light bonfires, memorahs or Christmas trees.

Washington is a town of marble halls, historic houses, ceremonies and celebrations. Christmas trees here have to be taller than most places - the White House Christmas tree is 20-feet high to scrape the medallion in the center ceiling of the Blue Room. In Christmas past, sometimes the trees have been so pretentious and pompous as to seem inappropriate to the story that begins, after all, in a stable. But this year, there is a reutrn to the homemade, the handmade, Christmas tree ornament, celebrating the traditional values of humanity, humility and compassion.

One of the most beautiful trees decorating official Washington stands in an alcove of the grand foyer of the Vice President's residence, Joan Mondale is a potter and an art historian who has decked her tree with more than 50 ornaments by some of the country's best craftsworkers.

Mrs. Mondale asked Paul Smith, director of the Museum of Contemporary Crafts in New York CIty, to invite craftspeople all over the country to make an ornament to lend to the Vice President's home for this season.

And they did, each according to his talents, celebrating, as Mrs. Mondale put it, "the vitality and creativity of the American imagination." On the tree with its base wrapped in a quilt are:

Elizabeth Gurrier's soft sculpture angel; Stanley Lechtzin's copper and silver-plated cutout ornament; Mary Ann Scherr's "Stars and Stripes" mobile star; William Harper's silver cloisonne enamel "Christmas fetish"; William Accorsi's Santa Claus on a sled made of rulers; Arline Fisch's crocheted silver mesh ornament; Harvey Littleton's teardrop glass ornament; beaded dolls by Navajo Indians and a cornhusk doll by a Seneca. On a table is a creche of batik figures made by Josie Neal of San Antonio, Tex.

Joan Mondale said, in reflecting on the ornaments, "In this age of mass-produced, machine-made products, the crafts put us in touch with our own individuality. They inspire that spirit of communication between creator and us that is affirmed each time we use a mug, a plate, a copper kettle . . ."

By tradition, the White House tree always stands in the Blue Room - perhaps because in Abigail Adams' day it was the only living room well-finished. This year New York decorator Mark Hampton kept all the decorations in the grand hall very low key, "suitable to a great house, but not a public building. You have to be careful in that great pompous hall not to obscure the architecture."

By direction of Rosalynn Carter, the tree is the star of the show. Mrs. Carter had it decorated with 2,500 ornaments made by retarded persons from all over the country.

Previewing the tree last week, the First Lady touched the ornaments as though they were frankincense and myrrh instead of a tiny doll with fur collar, a needlepoint ornament, a straw flower, a ball stuck with toothpicks, a gilded, egg-shaped pantyhose carton, a silvered pine cone and a worm made of pipe cleaners.

She spoke of the imagination of the retarded and her hopes that everyone can have the opportunity to learn as much as they can and go as far as they can. And she talked a bit about making popcorn and paper chains with her children, when they lived in less public houses with private Christmas trees. And how this year, daughter Amy decorated the lowest branches of the tree in the family part of the White House. (The Carter's private family tree with their favorite ornaments will be decorated in Plains, where they'll spend Christmas.)

A sidelight to the tree viewing: As people left the White House, they passed a nook where pigeons were gobbling up the remains of a bag of peanuts.

At the Octagon, built in 1799, Jeanne Butler has decorated the tree with antique toys. Decatur House, the Woodrow Wilson Home, Woodlawn Plantation all have their Christmas decorations, appropriate to their age and situation. Mt. Vernon has no tree, because trees were not yet popular during George Washington's day.

At the Smithsonian's Museum of History and Technology, at 14th Street at Constitution Avenue, there are 12 trees for Christmas.

One especially pretty tree comes from a Ukrainian tradition, according to Helen Gunderson. A woman who was too poor to decorate her tree welcomed the help of the house spiders. On Christmas morning the sun shone through, turning the spiders and their webs to silver.

Sunny O'Neil of Bethesda has decorated the Victorian tree with not only the cookies, candies and gilt pine cones you'd expect but also small flags and crocheted snowflakes. The pioneer tree, by the Fairfax County Extension Homemakers, is hung with pomander balls made of apples stuck with whole cloves, yarn dolls and rings. The 18th century-style Tidewater Plantation tree, by the Evergreen Green Club of Georgetown, has miniature needlework figures and gilded English walnuts on strings, all topped with a crown.

The Williamsburg Folk Art tree by Lawson Carr, Edna Penell and the Flower Cupboard of Williamsburg and Smithfield, Va., uses seashells made into ornaments and small wreaths, and a starfish stands in for a star. Mrs. Harry Harris spent five years making the 150 ornaments inspired by Carl Faberge for the Russian tree. The French tree of paradise is a topiary trimmed with apples, paper roses and communion wafers. The Italian version is a pyramid, called a ceppo not a tree al all, to hold a creche, angels, candles, gilded fruit and a madonna. The tree of Brazil, a bare-branched deciduous variety, has foil tassels and silver stars. The tree on Denmark by the Danish Club of Washington has straw hearts and garlands and Danish flags.

Over at the Pentagon one year they made garlands out of computer tape. In Belize, in Central America, a Foreign Service couple decorated an imported pine with double hibiscus flowers, renewed every day. The Metropolitan Museum of Art uses Neopolitan Christmas crib figures from the second half of the 18th century. One officd used an umbrella tree festooned with a rubber alligator. In a 16th Street front hall, the rubber trees all wear red silk balls.

The tattered paper chain brought home from kindergarten, the gilded fan from the trip to Japan, the china doll head sans body from grandmother's trunk, the threadbare bear loved not wisely but too well, the tin angel from Mexico, the pewter angel from the Viennese tour of duty, the peppermint canes that melt away before Christmas, the lights that one by one burn out, the copper star on top that has to be re-orbited every day - of such mysteries is the holiday made.

Christmas decorations and trees are on view on holiday schedules at the White House, 10 a.m. to noon, Tuesday through Saturday; Decatur House, 740 Jackson Pl. NW from 10 a.m. to 2 p.m. weekdays, 12 to 4 p.m. weekends, candlelight tours 7 to 9 p.m. Dec. 19 and 20; the Octagon is open 10 to 4 p.m., Tuesday through Friday, 1 to 4 p.m. weekends; Woodrow Wilson House, 2340 S St. NW, is open 10 a.m. to 2 p.m., 12 to 4 p.m. weekends. The Museum of History and Technology is open 10 a.m. to 5:30 p.m. every day. Woodlawn Plantation and Mt. Vernon do not have Christmas trees. More trees on Pages N5 and N6.