A VISIT TO Kenmore, one of the country's most beautiful and oldest house museums, transports you into the 18th-century world of George Washington, his only sister, Betty, and her husband, the multi-talented Col. Fielding Lewis.

The story unfolds in Fredericksburg, Va., about 50 miles or an hour's drive from the Washington area. At Kenmore, amid the dogwood and oaks, you are enveloped in the charm and elegance of the house that Lewis -- a planter, land surveyor, land speculator, ship merchant and member of Virginia's House of Burgesses -- built for Betty.

Kenmore typifies the Colonial architecture of the mid-18th century, believed to be based on pattern books available to builders of the period. Houses were based on Old World models but were adapted to the needs of the New World. Existing records suggest that Kenmore was completed in the 1750s, sometime after Col. Lewis and Betty Washington were married in 1750, uniting two families who had settled in the Northern Neck of Virginia in the 17th century.

Betty, who was actually one of Lewis's cousins, apparently had known him quite well already, and after his first wife, Catherine Washington, died, Betty is said to have been attracted to his young son, John Lewis. Records suggest that the two remained close throughout her lifetime; after her death in 1797, John Lewis inherited Kenmore.

Besides the interesting family history that the Kenmore guides intertwine in their narratives, the house is architecturally significant for its interior decorative plasterwork. The embellished interior, in which the major rooms are plastered rather than paneled, contrasts neatly with the simple, unadorned brick exterior of two-foot thick walls. Kenmore's dining room has the distinction of being included in Helen Comstock's "100 Most Beautiful Rooms in America."

The dining room features one of three spectacular hand-carved plaster ceilings that create a feeling of elegance throughout the house. The master chamber's ceiling, known as the "Four Seasons Ceiling," depicts a plant symbolic of each season: palm leaves for spring, grapes for summer, acorns for fall and mistletoe for winter.

The two-story house, for which no exact construction date has been documented, is attributed to John Ariss, but no proof has been found. The origin of the plasterwork remains one of the great enigmas of America's decorative history. Family records refer to the craftsman only as the "stoco" or "stucco man," a plasterer whom Kenmore shared with George Washington's Mount Vernon.

Lund Washington, the president's manager at Mount Vernon, wrote letters describing his considerable pleasure with the work, but also the plasterer's slow execution of it: "October 15, 1775: The stoco man thinks he shall be four weeks in the dining room. The ceiling is light and handsome. It is altogether worked by hand which makes it tedious. I can form no judgment how long it will take him. Mrs. Washington intends to talk to Col. Lewis on her way down about it."

Visitors enter Kenmore through the Crowninshield Museum. Here, you can view original Kenmore furnishings, family memorabilia and examples of decorative arts that could have been used during the mid-18th century. A diorama of 18th-century Fredericksburg explains the history of Kenmore during the Colonial period.

A visit to Kenmore culminates in the kitchen, where free tea and gingerbread are served. The tradition developed from an account of a visit by the Marquis de Lafayette to Mary Washington, whose original gingerbread recipe is used. KENMORE --

1201 Washington Ave., Fredericksburg, Va. 703/373-3381. Open 10 to 4 daily December through February (closed Dec. 24, 25 and 31 and Jan. 1) and 9 to 5 daily March through November. Admission is $4 for adults, $2 for ages 6 through 16 and free for ages under 6 and Kenmore Association members; group discounts available. Take I-95 south to Route 3 East into Fredericksburg and follow the signs to Kenmore. An exhibit of gingerbread houses will be on view in the Crowninshield Museum through Dec. 30.

Alexandria freelance writer Harriet Edleson enjoys visiting old homes.