It's hard to say exactly what it is about snow and sleet, old year going, new year coming, that makes people think about the leftovers of other centuries.

Perhaps it's because people stay inside in the bad weather, give more dinner parties and are thus encourage to count the silver, take stock of their possessions and plot to acquire more.

At any rate, the evidence is in. This is the season for the big antique shows and sales. The 24th annual Washington Antiques Show for the Thrift Shop charities will be held Jan. 10-14 at the Shoreham Americana. The 25th annual Winter Antiques Show benefiting the East Side Settlement House will be held Jan. 26-Feb. 4 in New York City.

Antique sales are soaring. The Gray Letter, an antiques "insider's report," puts the 1977-1978 season's turnover in antiques (including auction sales, shops, etc.) at $5 billion. Christie's Inc. in New York City reports that its 1978 fall sales doubled over 1977-$21.6 million to last year's $11.6 million. Worldwide, its total is $55 million, a 55 percent increase. Sotheby, Parke Bernet figures show a 50 percent increase over last year, worldwide, for a total of $143.3 million. The New York total was $51.3 million, still under the London mark of $60.4 million U.S. sales amounted to $56 million.

In Washington, Weschler's and G.C. Sloan Auction houses are up as well. Benjamin Weschler says his house did about $4 to $5 million in business, not counting four or five big real estate auctions that included one million-dollar sale on the Eastern Shore.

Donald Webster at G.C. Sloan's said his auction-house sales totaled about $1.5 million.

Even the auction house of Theriault of Waverly, Pa., Specialising in toys, set a record last month. A wind-up tin toy, "Juggling Popeye and Olive Oyl," that was made in about 1960 in Japan sold for $600 to a New Jersey toy collector.

That's not all. As a matter of fact, the big news in antiques this year is not how much more money is being made from a new phenomenon. Antiques education is the fastest-rising segment of the antiques market. Scholarship in the decorative arts isn't at all limited to museum professionals. Today, the enlightened collectors are likely to be young, professional two-salary families. They not only want to buy antiques, but they want to know what they're buying.

The burgeoning market in antique books is easy to see. The big change is coming in the sort of antique books being published. Losts of beginner books: The history of anitques of the world in 250 pages, sure, but more interesting are the great number of books on esoteric subjects-the new book on "Art Nouveau Lighting," for instance, by Alastair Duncan (Simon and Schuster); "Tiffany Silver" by Charles M. Carpenter Jr. with Mary Grace Carpenter (Dodd and Mead); "China for the West," by David Howard and John Ayers, a two-volume set (Sotheby).

This year also has seen two new antique magazines come on the news stands Antiques World and American Art and Antiques. Antiques Monthly has gone to twice-a-month publication.

The great popularity of the recent museum decorative arts and artifacts exhibits, principally King Tut and the Splendors of Dresden, are among the strongest evidences of the great interest today in the objects of the past. Objects which have been handled and used-a tea pot, a wooden stool, a necklace-carry with them a fascination that is more easily understood than the more abstract art for art's sake.

And there is a whole winter season of forums, seminars and other education programs scheduled from New York to Hilton Head Island, S.C.

Elizabeth Shaw of Christie's says that most of the sales increase came from the high quality of sales-by which she means people paid more money for the individual objects.

Art Nouveau and Art Deco prices were up 300 percent a Christie's. One Tiffany peacock lamp, commissioned by Charles Gould, brought $77,000 recently-sold to the Sydney and Frances Lewis Foundation of Richmond. The lamp, called one of the most important Tiffany objects to be sold in a decade, is now on display in the Virginia Museum's Art Nouveau Gallery, Richmond. Shaw says the lamp was sold in 1946 by the Tiffany Foundation for $225. A Tiffany favrile glass and bronze flowering lotus blossom lamp sold for $60,000 at Sotheby Parke Bernet no long ago. And in September at Monte Carlo, a new auction record was set for Daum glass at $32,400. A set of Louis Marjorelle Art Nouveau furniture went to a Florida collector for something over $32,000. Another big Art Nouveau sale is coming up at Christie's on Feb. 17.

Ironically, as a spinoff from the interest in Art Nouveau, the gaudy pieces of late 19th-century eclectic-the excessive ornamentation that brought on Art Nouveau as a revolt in design-are bringing high prices. A 63-ounce centerpiece with an oval vermeil bowl, decorated with an exotic bird and its nest, brought $1,300 at a recent Phillips auction.

At a recent sale of American furniture, most pieces were bought by dealers for resale, setting new records on price. Israel Sack Inc., a New York dealer, for instance, paid $176,000 for a pair of Philadelphia Queen Anne walnut chairs. The same company paid $154,000 for an 18th-century Goddard-Townsend kneehole desk made in Newport, a new record for a single piece of made-in-America furniture.

A great many foreigners are buying in New York, pushing the auction sales there up to the level of London and leading many people to believe New York has succeeded London as the antiques capital of the world. Londoners, of course, disagree, and since antique-sale figures are notoriously difficult to come by, it's hard to say which is which. Most foreign buyers seem to be most interested in buying back their own country's heritage.

A 14th-century Chinese porcelain ewe, for instance, sold recently for $286,000 at Christie's to a Hong Kong dealer. The National Museum of Ireland bought back a pair of rare Irish Chinoiserie silver bowls for $19,800 on Dec. 6 U.S. prices for European silver seems to be lower than prices in England, so more British and European buyers are coming to New York, according to another auction house, Phillips of New York. Their bids pushed up prices by about three times the expected at a Dec. 7 sale at Phillips.

Autographs, books and letters are selling well. At Sotheby Parke Bernet recently a record was set with the sale to Focus magazine for $85,000 of an autograph log kept by the co-pilot of the "Enola Gay," the plane that dropped the atomic bomb on Hiroshima. A letter written by President Lincoln to Gen. Grant, asking to enlist his son Robert Todd, was bought by Forbes for $32,000, a record for a Lincoln letter.

The variety of things sold continues to expand with "who-would-have-thought-it" auctions. Late 19th-century to 1920s dresses sold briskly at the first specialized antique clothing sale Nov. 21 at the Sotheby Parke Bernet. Nine lace and overlaid dresses from the '20s brought $450, and a taupe silk two-piece dress from the 1890s went for $375, considerably over its estimated $80 to $120.

In Washington, "What were selling is changing as well," says Benjamin Weschler. "Our regular auctions last year were totaling about $10,000, now they're up to $20,000. So many young couples are moving to the city they want to buy the big old Victorian pieces to suit their high-ceilinged row top house. Oak furniture is another style that's increasing in demand. The other day, at one of our regular Tuesday sales, we sold an oak bed for $1,000. It hasn't been many years since it would have brought $50."

Donald Webster of Sloan's says, "We are seeing a great many English dealers coming over to buy English furniture and the decorative arts. Paintings and rugs are up with us as well."

Everyone is speculating as to what the opening up of China will do to the market in their magnificent antique objects.

So what's not selling? European and continental porcelain, 18th-century silver, French Empire furniture are all considered currently devalued. But that was yesterday-tomorrow they'll likely be up, too, if the market keeps going the way it has.

With the prices like these, no wonder people are flocking to lectures and forums to learn more about the art of buying antiques. What follows is but a sampler of the uncoming events:

The Washington Antique Show has a number of educational programs scheduled. Ivor Noel Hume, director of archeology at Colonial Williamsburg, will speak at 11 a.m. Jan. 11 at a luncheon on "New Roots for an Old Tree: Discoveries at Carter's Grove." Hume has recently found what is believed to be the remains of an early settlement on the river banks at Carter's Grove, with fascinating material on the difficulties of life during that period when 40 was old-about-to-die.

Clement E. Conger, White House curator, will speak Jan. 13 at Young Collector's Night on you know what-including no doubt a pitch for the new White House effort to build a $20-million endowment to buy paintings and other decorative delectables for the presidents' house.

Desmond Guiness, president of the Irish Georgian Society of the Irish Republic and author of "Irish Houses and Castles," will tell how those magnificent mansions are being restored-thanks in part not only to Arab oil-rich nabobs but also to Dutch vacationers who buy them for second homes. And, surprise, from Irish families now making money from selling their vegetables in the Common Market. He speaks at 11 a.m.

A panel of exhibitors will describe their wares at a roundtable from 6 to 8:30 p.m. Jan. 12. More to the point, verbal appraisals will be made on four days: silver, Jan. 10, by Malcolm Stearns; porcelain, Jan. 11, John Hart; prints and drawings, Jan. 12, Frank Schwartz; brass, Jan. 13, William Blair.

A loan exhibit of prints, paintings and architectural renderings of Lafayette Square will be on view at the show. A catalogue of articles about the history of the square will be sold. Information and tickets are available from the Washington Antiques Show, 6412 Brookside Dr., Chevy Chase, Md. 20015.

Antique forums are nothing new-the Williamsburg Antiques Forum on the Arts in Early America celebrates its 31st session this year. But there are more people than ever attending these events-better than twice as many as in the original session-so much so that Williamsburg is planning several spinoffs.

Jan. 28-31 and Feb. 4-7, Williamsburg will concentrate on "The Decorative Arts of the 18th Century," certainly the Virginia town's strong point, Michael Archer of London's Victoria and Albert Museum and Ivor Noel Hume, Williamsburg's resident archeologist, will speak at both sessions. Four workshops will be held on furniture, textiles, ceramics, silver and metalwork from the local collections. The new interest in conservation is recognized by panels on preserving and restoring furniture and accessories, paintings, textiles and paper.

Feb. 1 through Feb. 4, Williamsburg will offer a mini-course, "An Introduction to Antiques," with six talks, a tour and workshop. Hugh DeSamper said he was interested to hear from one such group that they wanted "more lectures and less food."

Jan. 2 March 18, "Wintertime in Williamsburg" will offer six all-day seminars every week planned around music on Mondays, plantation life on Tuesdays, decorative arts on Wednesday, colonial architecture and gardens on Thursdays, restoration and archeology on Fridays and colonial crafts and trades on Saturdays. From a recent sampler day at Williamsburg, it was early to see that the crafts program is likely to be the most popular.

The cabinetmaker will show his workshop and discuss Williamsburg furniture on Jan. 6 and March 3; the printer and bookbinder on Jan. 13, the cooper, Jan. 20, musical instrumentmaker, Jan. 27; the silversmith and foundry, Feb. 3 and March 10; the gunsmith, Feb 10 and March 17; domestic crafts, Feb. 17 and the blacksmiths, Feb 24. Escorted architectural tours are included in the programs. More information is offered by the Williamsburg Antiques Forum, P.O. Box C, Williamsburg, Va., 23185.

The Fifth Annual World Antiques Market Conference Jan. 26 and 27 in New York City at the Waldorf-Astoria will hear Chris Delaporte, Heritage Conservation and Recreation Service; William Lehrfeld, a Washington attorney who specializes in taxation; Robert Bishop, director of the Museum of American Folk Art, as well as a collection of American and European dealers and collectors. The event is sponsored by Antique Monthly, P.O. Drawer 2, Tuscaloosa, Ala. 35401.

The newest entry is the second annual Sea Pines Plantation Conference on American Antiques on Hilton Head Island, S.C., Feb. 21-25. "Discovering the American Past" is the theme with Wendell Garrett as program chairman. Speakers will include Jane C. Nylander, curator of textiles and ceramics at Old Sturbridge Village; her husband, Richard C. Nylander, curator of the Society for the Preservation of New England Antiquities; Mervin B. Martin, furniture conservator of Winterthur; and Kenneth M. Wilson, director of collections and preservation at the Henry Ford Museum, among others. Probably the biggest attraction will be the excursions to private collections in Savannah, Ga., and Charleston, S.C. More information from Sea Pines Plantation Co., Dept. D, Hilton Head Island, S.C 29928, phone 803-785-3333.

The Smithsonian Associates has lectures year around on the decorative arts. Paul N. Perrot, assistant secretary of the Smithsonian for museum programs, will moderate a series of eight lectures on 3,500 years of glass beginning Jan. 25. William A. MacDonald, professor emeritus of art and archeology at George Washington University, will give a course on oriental rugs beginning Feb. 14. Jane T. Griffin will moderate a course on the arts of China-sure to be important, beginning Jan. 22. For a complete schedule, call the Smithsonian Resident Associate Program, 381-5157.

Speculation is that with the continuing inflation, people are buying antiques as a hedge. But Shaw says she suspects it may be simpler than that. "Antiques are well made-the shoddy pieces fell apart long ago." CAPTION: Picture 1, Above, an American Federal sofa; Picture 2, a weathervane; Picture 3, 4, a washstand and a sideboard at the Washington Antique Show. Picture 5, 6, Also, a paperweight lamp and jewelry from a Weschler's auction catalogue; Picture 7, A Tiffany lamp; Picture 8, A pair of Queen Anne Walnut side chairs.