Just because you live in a 1957 house in the heart of Colonial Williamsburg, you do not have to furnish "in period."

Beatrix Rumford, who is director here of the Abbey Aldrich Rockefeeler Folk Art Museum, now lives in the white gambrel roof frame house that belonged to Col. John Tayloe, a rich and influential planter in colonial Virginia until 1773.

It is one of the non-exhibition original houses in the restored Virginia capital, and Colonial Williamsburg not only leases it to Rumford for her private dwelling but also keeps it in good repair, handling all plumbing, painting and plastering problems, and grounds maintenance. This service has proved a boon to this busy museum director, who says a 220-year-old house can be full of surprises, and she'd hate to be coping with them by herself.

In appearance, the basic house remains almost unchanged from the 1750s. It fine interior woodwork, including wall paneling, bespeaks the best the colonial builder had to offer in design, materials and craftsmanship.

When Rumford moved in a few years ago, she looked at the worn treads on the stairs and wondered how two centuries of Tayloes, Pitts, Tazewells, Madisons, Griffins and Colemans - the successive families who lived in the house - had used its rooms and furnished them.

Although a few original items remain, the present occupant knew she could not furnish the house in the Chippendale and Queen Anne styles of its architectural period becuse of present-day costs.

So she moved in, she says, with a "great combination of all sorts of things-english, American, and Oreintal - combined currently in this 18th-century situation, to my own taste."

She has furnished with some American Empire pieces, of which her living room sofa is a good example, because she has found them still affordable and still, she feel, undervalued on the market.

"I never really spent an enormous amount on anything. The most I have paid for anything is $2,500 for the corner cupboard in the dining room. I still think you can acquire interesting and good peices if you are prepared to spend a lot of time looking, and then upgrade all the time and not be afraid of change. If you have a well-developed eye, of course, you have a head start."

The development of her own "eye" began when she was 16, and her great aunt advised her to begin a collection to cultivate her taste, train her eye, and learn to distinguish the old from the new. She chose horse brasses, and never paid more than $5 for any one of them. Today they are lined up over a passage opening and she still delights in them. They remind her that a museum director can begin her own development in sometimes modest ways.

She terms herself these days an "accumulator" rather than a serious collector - a "happy eclectic" who likes all sorts of things from many periods, and who knows how to mingle them artistically. "I am opposed to clutter, though, so I retire things from time to time, and shift pictures ans accessories now and again. I always keep a spare look, though, and I love my upstairs white walls."

Woodwork in the house, including paneling, cornices, stairs, and most doors, is painted in the well-researched original 18th-century colors.

She purchased bird prints by George Edwards, and English naturalist, for 2 pounds each at Portobello Road market in London and made a "permanent investment" in their frames, done in the 19th-century manner, with gold leaf frames and mats of reverse painted black glass.

"If you are attracted to old things, it is a great privilege and a joy to live in an old house. It offers a very congenial atmosphere," says Rumford. "I am a stickler about two things: dressing my fireplaces and my four-poster beds correctly. I feel it's worth making the necessary investment to make both hearths and beds look complete and properly finished in every detail."

If yo u are fortunate enoung to own a four-poster bed, Rumford's advice is to spend your money on the right fabrics and shirred or gathered canopy valances and bed ruffles, and give careful attention to the prints and plain colors that are used together and to the quilts or woven coverlets that you choose to use as bedspreads. Generally, she says, window fabrics are repeated for the bed hangings.

One rule to remember , she says, when dressing a fireplace, is to choose andirons that are in proper proportion to the fireplace opening. Their height should be from 1/2 to 3/4 the height of the opening, their shafts should not extend beyond the face of the fireplace, and they should be spaced so there are inches to spare from the foot of the andiron to the side of the fireplace.