A public hearing on a draft master plan and ordinance for historic preservation will be held May 21 at 8 p.m. in the council hearing room in Rockville by the Montgomery County Planning Board and the County Council. A public forum to discuss plans for historic preservations is scheduled May 9 at 8 p.m. in the Silver Spring office (8787 Georgia Ave.) of the county planning board.

Financing of $4.5 million for construction of 30 contemporary houses in the Oakton area has been arranged for Sante Fe Development Co. by James T. Barnes of Washington D.C. Inc.

Construction and permanent mortgage financing of $1.6 million each has been arranged by National Capital Copr. of Washington, based in Chevy Chase, for a 10-court racquetball club being built on Montgomery Avenue in Bethesda by a group headed by Roger W. Eisinger and John K. Kilbane, who are also principals in the nearby multi-building "air rights" office complex.

Sale of the building at 1335 Piccard Dr., Rockville, by Fields Road Partnership to Solar Building Associates for $1 million was negotiated by Peter Larson of Shannon & Luchs. The building will become the headquarters of Solarex, a solar development firm that had been leasing the space.

Greenhorne & O'Mara Inc., an area-wide engineering and architectural firm, recently increased its headquarters space in Riverdale. The 29-year-old firm, which was 350 employees, also has offices in the City of Fairfax and in N. Hungtindon, Pa.

The seventh annual Takoma Park house and garden tour will be held Sunday from 1:30 to 5 p.m. Several newly renovated houses will be shown. Tickets may be purchased Sunday after 1 p.m. at the municipal building, 7500 Maple Ave., for $3.50. For information, dial 589-5437.

Carter W. Boehm, president of Century 21 Townside Properties in Alexandria, has announced that his firm has changed franchise affiliations to become Townside Partners, the first new Partners real estate franchise to be operated in this area.