BREAK OUT your calling cards, folks. It's open-house time all around town and country. This year's selection of holiday house tours promises plenty of good old-fashioned Christmas hospitality.

* There'll be a candlelight tour, with music and refreshments, at the London Town Publik House from 7 to 9:30 p.m. this Friday. The tavern is at 839 London Town Road in Edgewater, Maryland. $3, $2.50 for seniors. 301/956-4900.

* The Columbia Historical Society is hosting free candlelight tours of the Victorian-decorated Christian Heurich Mansion, Friday and Saturday from 5 to 7. The Barry Trio and Close Enough Barbershop Quartet will entertain visitors, and cider will be served. The mansion is at 307 New Hampshire Avenue NW. 785-2068.

* The Alexandria Tourist Council has organized a tour of four Old Town Alexandria historic homes and a tavern, all trimmed in period decorations and reverberating with old-time music. The tours are Friday and Saturday, beginning at the Ramsay House Visitors Center, 221 King Street. Tickets are $8, $5 for children between 6 and 17, and will be sold between 5 and 8 both days. 549-0205.

* "Christmas at the Inns" is a free tour of three sturdy old bed and breakfasts -- the Inn at Antietam and the Piper House Bed and Breakfast in Sharpsburg, Maryland, and the Thomas Shepherd Inn just across the Potomac River in Shepherdstown, West Virginia. They're open Saturday from 10 to 4, and refreshments will be served. 797-1862.

* Historic Chestertown, Maryland, hosts its annual Christmas walking tour of 14 homes and public buildings from the 18th, 19th and early 20th centuries on Saturday from 1 to 5. Tickets are $12.50, $5 for children under 13, and can be purchased at Emmanuel Church on the day of the tour. Call 301/778-0866 for more information.

* The William Paca House Christmas celebration is Saturday and Sunday in Annapolis. There'll be food prepared the 18th-century way and continuous live performances of period music on dulcimer, harp and violin. Hours are 10 to 6 (by candlelight from 4 to 6) Saturday, and noon to 4 Sunday. At 186 Prince George's Street. $3.50. 301/263-5553.

* The staff at Woodlawn Plantation in Mount Vernon dons period garb to present Carols by Candlelight, a re-creation of an 1819 holiday party, on Saturday from 7 to 10, and Sunday from 3 to 6. There'll be madrigals, a yule log, carriage rides (Saturday only) and refreshments. Admission is $4, $2 for children under 18. 557-7881.

* Rockville Civic Center Mansion, decorated Williamsburg-style, holds open house Sunday, with choral and instrumental music, exhibits on local history, a candlelight tour and a reading of a children's Christmas story, all from noon to 4. At 603 Edmonston Drive, Rockville. 424-3184.

* Oxon Hill Manor holds a free open house Sunday from noon to 5, with a children's choir, handbell ringers and other instrumentalists. Crafts and refreshments for sale. At 6901 Oxon Hill Road, Oxon Hill. 839-7783.

* Belle Grove Plantation presents a living history interpretation of holiday preparations in an 18th-century home, with tea, cookies and music. Hours are 6 to 9 Monday through December 21, and 1 to 9 December 22. $2.50, free for seniors and children under 16. 703/869-2028.

* The sixth annual Christmas Homes Tour of five historic and contemporary homes (and the Arnold Grove Church) in Hillsboro, Virginia, is from 1 to 7 Saturday, with a candlelight tour at 3 p.m. There'll be a crafts fair at the Old Stone School (you can sit down to a hot lunch at the school for $3.50), and traditional American holiday music throughout town. $8 for the whole tour, $2 for individual homes. Hillsboro's on State Route 9 about 10 miles west of Leesburg. 703/777-0519.

* There'll be candlelight tours (refreshments provided) of the Victorian-decorated Oatlands Plantation, Saturday from 6 to 9 p.m., $5; and daytime tours (also with refreshments) of the mansion through December 24, Mondays-Saturdays from 10 to 5 and Sundays from 1 to 5. $4, $3 for seniors and children 7 to 18. Arts and crafts of more than 100 area artists will be shown in the mansion's carriage house during regular daytime hours. Oatlands is on U.S. 15 six miles south of Leesburg. 703/777- 3174. Katherine Seigenthaler.