After all these years of being called a trailer and then a mobile home, the factory-built, modular dwelling is becoming an immobile home.

In fact, Ed Parish of San Jose, Calif., who heads the Immobile Home Co., which is developing small communities of "immobile homes," contends they can be sold for 20 to 30 percent less than conventional stick-built houses on their own lots. Depending on the cost of the lot, Parish says, immobile homes can be sold profitably on 48-by-80-foot lots for $40,000 to $60,000.

Parish, who got his start in the business by selling single-wide mobile homes to persons who put them on rented spaces in mobile home parks, insists that the 1980s' version of the sectional, factory-built dwellings will be a principal and less expensive alternative to conventional houses.

"As long as we can deliver factory-built houses that are priced $12,000 to $15,000 below comparable site-built, conventional houses, the market will be good in normal conditions."

However, Parish admitted that sales have been sluggish, just like the conventional home market, in recent months.

In outlining the Immobile Home Co. procedure to a Washington group recently, Parish said that he and his partners came up with the plan of using a stick-built garage attached to the factory-built sections to make the houses attractive to Western and Southwestern buyers. Basically, the technique is to lay out permanent sites for one, two or three factory-built house modules on a small lot and build a one or two-car garage adjacent to a front section.

In addition to selling the houses that range generally from 1,032 to 1,568 square feet of living area, the Immobile Home Co. creates a community with a swimming pool, clubhouse, tennis courts and other amenities.

"Studies showed that fewer than 2 percent of all mobile homes were ever moved after being put on a site, so we decided to pursue the immobile home aspect and use newer designs with slanted roofs and overhangs," Parish said. He said consumer studies showed a preference for "more residential" exterior appearances, a garage to avoid tandem parking alongside a mobile home and more privacy.

"We provided more privacy by using the California technique of zero-lot-line zoning to build one unwindowed side of the house tight against the next lot to provide a private yard on one side of every house," Parish said. "To provide some light on the windowless side, we put skylights into the roof."

Parish said that the Immobile Home Co. now is ready to franchise its technique to other sellers of mobile homes who want to develop communities of immobile homes.

In the Washington area, a mobile home community of dwellings on permanent sites has been in the planning stage for a site in the Germantown area of Montgomery County. Also, there are expectations that some new communities of permanently placed mobile homes may be started in Fairfax County.

Jack Wynn, a spokesman for the Manufactured Housin Institute, said there are at least 300 subdivisions of permanently placed mobile homes on owners' lots throughout the nation.Agreeing with Parish, Wynn said the market is moving eastward.