Four large houses near the courthouse complex in downtown Rockville could be mistaken for restored dwellings in that historic district. But they are really the offices for eight small law firms.

The 15,000-square-foot Adams Center, as it's called, was completed last summer by homebuilder John duFief.

The Montgomery County builder said that after weathering the 1973-74 housing slump here, he decided to "investigate potential sources of income for periods of slow residential sales. I was interested in creating long-term investments that could provide income after retirement."

DuFief said that small-volume builders of custom homes priced over $250,000 traditionally face lean times when tight money and high mortgage rates soften their normal markets. Some of the larger-volume homebuilders in Potomac and other areas have done some commercial building in periods when the exceptionally cyclical home-building industry is on the downswing.

"We suffer an even larger share of the malaise in housing sales than do the high-volume builders of tract houses," said duFief, who usually builds only two or three houses a year -- with a small crew that now includes his 21-year-old son.

In a time when mortgage rates have broken all former barriers, duFief is working on only one new house in Potomac and building additions.

His major interest, Adams Center, which he began planning three years ago, is providing financial security and is the inspiration for a similar project he is thinking about building.

"I was fortunate in finding an acre-plus off North Adams Street" for the Adams Center, he said. "An old house had been burned down (by vandals) and the site was transitional between business and residential.

"My architect, Duane and Duane of Rockville, work with the city's Historic District Commission on plans for the site," which is within walking distance of the courts and county government offices, he said. "We came up with four large houses, two quasi-Victorian and two in the federal style."

DuFief owns a substantial percentage of the $750,000 Adams Center, and his partners are the law firms that are located there.

"They were with me in the Adams Center Partnership from the beginning, and that provided a 100 percent commitment for leasing before ground was broken. Thus, it was not the usual gamble with an average commercial or speculative residential property."

"Another advantage," he continued, "was the ability of the architect to design the iinterior to meet specific needs of the occupying law firms. Our office suites are equipped with libraries, fireplaces and reception areas that suit the individual firms. One occupant wanted, and got, a kitchen and shower for a suite."

In addition to having rental income and some tax advantages, duFief said that his entrance in specialized commercial construction "also brought a sort of sabbatical change of pace and new challenges after 20 years of building homes for people." And the occupants are good tenants, he added, because they are part-owners with an interest in the property and its good maintenance.

The average rent is $7.50 a square foot, and the tenants pay their own utility costs. The buildings have wood shake or metal roofs, gas-fired heat and eletrical air conditioning.

Other medical, legal and other office complexes have been created to resemble traditional and contemporary town houses on small sites in varied suburban locations.

"But this one was especially important to the historic-district idea of Rockville," said architect Michael Patterson, chairman of the Historic District Commission of the City of Rockville. "I think it adds to the integrity of the historic district in the west end of Rockville."

Architect Frank Duane said that the painted brick exteriors, light colors with contrasting shutters and old-style porches provide a blend of historical federal and modified Victorian styling, plus a transition between nearby commercial and residential uses.

The site was formely part of the old Peters farm, north of West Montgomery Avenue.