The trend to renovating older houses continues to gather steam throughout the United States.

To help it along, "home fairs" offering information and helf for amateurs and experienced craftsmen have begun to be organized regularly.

Clem Labine, editor and publisher of the Old-House Journal, the nation's leading home-renovation periodical with 35,000 subscribers, points out that there already are major renovation fairs in Baltimore, Chicago, Macon, Ga., and Salt Lake City among others.

Good ideas very often come out of the home fairs.

A recent Chicago exhibition, "City House -- A Marketplace of Renovation Ideas for Old Houses," is a case in point. It was sponsored by the local chapter of the National Trust for Historic Preservation and the Chicago Commission on Historical and Architectural Landmarks.

Architects, contractors and experts on historic preservation advised audiences in seminars to do their best to preserve the romantic qualities of an old house rather than tearing out all of the nostalgia and starting anew.

Cynthia Weese, an architect with Weese, Seegers, Hickey, Weese, recommends that high ceilings in old kitchen be preserved for their beauty and good ventilation. Needed light can be added by putting lamps under cabinets or open shelves. She further advocates the use of under-cabinet refrigerators, freezers and dishwashers to maximize space.

Before going to an architect, Weese suggested, a homeowner should make a list of the things he or she wants to do, in the kitchen for example.

These might include whether he or she wants eating space as well as an area for food preparation, whether storage is needed (or can the pantry be used?), or whether a laundry room, not provided in the Victorian era, is needed.

Robert Furhoff, an interior designer, recommends that homewoners become as familiar as possible with the historic details of their homes. Wills, deeds and other documents will help them in this research, he said.

"Don't remove and replace windows," he advised, pointing out that often the whole character of a house can be changed by installing modern windows. He also recommends that before ripping out plaster, research should be started to learn what may be there. In some cases the walls were intended to be a combination of paneling and painted surfaces. When plaster is removed, the woods don't match.

When applying to a bank for a renovation loan, the homeowner should have the plans in mind and share them with the banker, counseled Joel Zemans, president of Mid-Town Bank of Chicago, who also recommended that a homeowner be in a position to tell the banker the prospects for the future of the neighborhood in which the house is located.

Walker Johnson an architect with the Chicago firm of Holabird & Root, said "the value usually increases when the property is maintained and the character not changed."

Johnson advises potential remodelers to "respect the sense of time and place," pointing out that it is the neighboring houses that make a street charming, not just a single home.

"Think of the house as a work of art which is not alterable," he added. "If you have an architectural monument, you'd want to maintain it. That's why painting or repainting must be done carefully."

The architect said that the trades that were used in the original house still are available. It is advisable to stay with the original trades, he added, instead of switching to an alternative, such as covering a building with new siding.

"Porches, windows, masonry, etc., should be saved rather than replaced," asserted Harry Hunderman, an architect with Historic Resources. He spoke about the details of the exterior and how they should be restored, emphasizing that it is important to know architectural terminology.

If original elements are unavailable or unsuitable, however, there are companies providing the industry with everything from gingerbread to order to stamped metal ceilings. Such firms have grown from 205 five years ago to some 830 in 1980. Labine of Old House Journal has predicted that before the end of this year, about 1,100 companies are expected to be in business, offering products to help those who want to restore older homes.