There's no shortage of things old and worn in these days of year-round flea markets and second-hand shops.

But old is not necessarily antique. To find treasure in all the trash, it helps to have either a practiced eye or a good buyers' guide.

The 1982-1984 edition of "GUIDE TO ANTIQUE SHOPS," which covers the District, Delaware, Maryland, Virginia, West Virginia, North and South Carolina, Tennessee, Kentucky, Alabama, Mississippi and Louisiana should be available by early December. It can be found at most local shops or by writing "Guide to Antique Shops," 125 East Street, Frederick, Maryland 21701 or by calling 301/662-6200. Its editor and publisher is William B. Anderson and the cost of the book is yet to be determined.

The "MEMBERSHIP DIRECTORY OF THE APPRAISERS ASSOCIATION OF AMERICA," which lists 1,200 appraisers in about 120 different fields from all over the country is available from The Appraisers Association of America, 60 East 42nd Street, New York, New York 10165 for $4. If you need recommendations about appraisers in your area, the association offers free referrals. Call 212/867-9775.

The ANTIQUE DEALERS ASSOCIATION OF MARYLAND distributes brochures of Maryland dealers to its member shops. To obtain a free copy, stop by a member's shop, telephone Bette Marshall at 948-3979 or write The Antique Dealers Association of Maryland, P.O. Box 303, Olney, Maryland 20832.

Here's a list of current antiques fairs, shows and auctions:

The NINTH WASHINGTON ANTIQUES FAIR will be held this weekend at the D.C. Armory. More than $12 million worth of antiques will be for sale by 185 dealers from 20 states. Wares include Ming vases, Tiffany lamps, Japanese prints and American folk art. It's Friday and Saturday from noon to 9 and Sunday from noon to 6 at 2001 East Capitol Street (next to RFK Stadium). Admission $3.50. Call 547-9215.

There's an art show and auction sponsored by the FINE ARTS GALLERY OF ARDMORE at the Norbeck Country Club in Rockville on Friday night. The preview is at 7:30 and the auction begins at 8:30. Admission $2.50. Proceeds benefit the Cashell Elementary School PTA.

Friday to Sunday will be the PURCELLVILLE HERITAGE ANTIQUES SHOW at Purcellville's Skating Pavilion. Featured will be oriental rugs and carpets, tools, paintings, Japanese wood-block prints and more. Admission $2.50. It's Friday and Saturday from noon to 9:30 and Sunday from noon to 6. Call 703/338-4521.

SHENANDOAH VALLEY HEIRLOOMS, objects and crafts from the 18th century will be exhibited Saturday and Sunday from 10 to 5 at the restored 1785 Burwell-Morgan Mill in Millwood, Virginia. The mill is one hour west of the Beltway on Route 50. Items on display include quilts, a case clock, painted dower chest and Southern silver. Call 703/837- 1799.

Antiquing to look forward to:

A collection of treasures from porcelains, brasses and silver to English and American furniture is featured at the sixth annual antiques show and sale at the McLEAN COMMUNITY CENTER, November 5 through 7 at 1236 Ingleside Avenue. The show begins at noon each day and the admission is $2.50. Call 790-9248.

Ninety of the East coast's finest antique dealers will exhibit their collections at the MOUNT VERNON COLLEGE ANTIQUES SHOW, November 5 through 7 at the Washington Hilton Hotel. Featured will be 17th- , 18th- and 19th-century American and continental furniture, rugs, clocks, paintings, prints, pewter, porcelain, silver, quilts and clothing. Admission $3. Call 331-3461.

The ANTIQUES AND COLLECTIBLES AUCTION held by the Sisterhood of Adas Israel Congregation will be held November 7. Items to be auctioned range from silver and art works to professional services and vacation packages. Admission is $5, which includes a catalogue and refreshments. It's at the Adas Israel Congregation, Connecticut Avenue and Porter Street NW at 7. Call 362-4433.