The best guarantee for a well-done restoration project is an educated homeowner.

A person who understands and appreciates the differences among architectural styles will not put a California Mediterranean door on a federal rowhouse.

And they are realistic about how competent they are with a hammer, saw, or mortar trowel and how much creative rehabilitation they can stand. They also know who to hire when they don't want to do the work. Knowing how to find and work with people in the building trades is one of their most valuable skills.

A good architect is one of their best resources. An architect is a professional in design who understands how buildings are put together. Architects are trained to think in terms of space and function, not rooms, and can work with you on planning the work.

They will do drawings, write specifications, help select a general contractor/builder, supervise the work as it is done, and hold your hand when things go wrong.

A general contractor/builder/rehabilitator is in the business of carrying out the work you want done. They are business people who understand the construction/rehabilitation process. They coordinate the work of the various subcontractors (plumbers, bricklayers, plasterers, electricians, roofers) so they arrive on time. They understand the requirements of local building codes. They are not, however, trained in design.

If you own an old house, even if it is not an historic one, you will want to hire architects and contractors who are sensitive to the qualities of old buildings. You will not want the oak baseboards and molding heaved out as trash because the workers and their supervisor did not appreciate their value.

The best way to find people who appreciate old building is from prople who have hired these people before or who have worked with them. Local historical societies, especially those who own house museums, can be excellent sources. Neighbors and friends of friends are good sources, if they own old houses. Banks, hardware stores, real estate brokers, lumberyard owners and suppliers of special millwork can also guide you.

Both the Northern Virginia and Suburban Maryland homebuilders associations have remodelers councils and will give you the names of their members. They will also send you a pamphlet, "How To Choose a Reputable Remodeler," produced by the National Home Improvement Council, 11 E. 44 St., New York 10017, will send "How to Remodel" if you send a stamped, self-addressed envelope.

Once you have a list, you will want to call each of the contractor/builders, describe the job to be done, and get the names and addresses of some previous customers. Go see the work, especially if it is a building like your own.

Talk to the owners. Ask about how the firm met schedules and deadlines, how they were to work with and if they cleaned up at the end of the day. Examine the details of the job, the corners and hidden places where it is easy to cover sloppy work. Check about the contractor's responsiveness to complaints and questions.

Most contractors are honest and want to do a good job. Your task is to learn to tell them from the other kind. One concern is stability.

Find out how long the firm has been in business or how long the owner has been involved with rehabilitation. Check with suppliers and contractors to see if they are paid on time. Be sure the firm is properly licensed and insured.