The Victorian renaissance is in full flower here. Begun in the 1980s, it is affecting single-family houses and whole neighborhoods, as homeowners in all walks of life tackle restorations and rehabilitations.

San Francisco has been called "the wooden city" because its unusual architectural character arose out of the abundant supply of redwood in northern California.

Unfortunately, after 1915, many of these old buildings fell victim to changing fashions in architecture, or to desecrators who stripped off all the ginger-bread and other embellishments for the sake of modernization. The plunder of the city's unusual hill neighborhoods included mass destruction of entire city blocks of deteroriated, but quality housing.

Then, like the three princes of Serendip, three young men joined forces to form San Francisco Victoriana, a company aimed at preservation of an architectural heritage.

The partners had a range of interests: Gary Kray, a native of the area, had a degree in history and a real concern about the dwindling stock of Victorian housing; Bill Lambert was trained in business and architecture; Gray Root's family had owned a cabinet shop.

From 1970 to 1972, they researched local Victorian architects and builders of the 1870s and 1880s, developed an extensive collection of rare pattern books on redwood millwork, and set up a custom millwork shop.

By this time there was a general reawakening of interest in Victorian architecture in San Francisco, but preservation efforts could only be viable, they reckoned, with availability of sound design knowledge of the period, and a supply source for necessary restoration materials and services. Their ambition was to offer both services.

The trio delved into the history, style and techniques of the period and collected an extensive library of old photographs, trade catalogues and books. They hired two full-time designers, a bookkeeper, three millwrights, a mill foreman, two plasteres, two contractors and three carpenters - and hung out their Victorian-style shingle.

The Victoriana partners and staff offer advice along with their moldings of wood and plaster, reproduction and antique lighting fixtures, wallpaper borders, doors, hardware and reproductions of newels, finials, shingles and other architectural pieces.

They provide a hour free appraisal at the showroom, general directions and conceptual design information. They also give free rough estimates of costs to clients who bring in photos of exteriors and provide a carpentry and installation referral service.

In the 4 1/2 years the firm has been in business, it has completed more than 60 building-front restorations, and handled hundreds of partial facelifts. From their experience they have developed a visual slide presentation, with history and style explanations, which they make available to preservation-oriented organizations for a nominal fee.

The partners lecture at the University of California in a course on San Francisco's Victorian architecture.

Yes, say the three partners, it is economically viable to restore old houses today. Victorian houses could never be build again economically. And mass destruction has shortened their supply. They claim that for every dollar spent on authentic restoration, the value goes up $3.

Most Victorian dwellings here are usually 25-by-85 feet and sit on a 25-by-110-foot lot, with four rooms up and four down.In 1880 such a house would have cost about $3,500 to build. Five years ago, it was selling unrestored for $45,000. Today, the same house would command from $80,000 to $100,000, unrestored.

Most owners spend an average of $10,000 to $14,000 putting back exterior embellishments, plus an additional $2,000 for a paint job. Some people have spent more than $100,000 for complete exterior and interior restoration.

"Today," says Lambert, "some of the houses that we have accurately restored are selling for $150,000 and up, as irreplaceable, historically important landmarks."

The partners in San Francisco Victoriana use no salvaged millwork or plaster from other buildings, because they do not want to encourage further demolition. They also allow no modern synthetics, such as plastics, to be used in their restorations, but insist on the type of materials used originally. They consider houses built from 1855 to 1920 within their interest range because they fall within the Victorian influence, even though they are outside the strict bounds of the period.

A catalogue, "San Francisco Victoriana Book of Authentic Mouldings," is available by mail for $1.50 from San Francisco Victoriana, 606 Natoma St., San Francisco, Calif. 94103. A second catalogue on redwood handrails, newel posts, and balusters is in preparation.