Eugene J. (Chick) Cullinane, son of the colorful late Leo Cullinane, has completed a model home in the $330,000 range. It's one of the Williamsburg-styled detached houses that he is building near the water at Mount Vernon on the Potomac. He even contributed some of his personally owned paintings and oriental rugs for the exquisite furnishing of the model. The site is on Ferry Landing Road. . . . For seven years the 22-year-old architectural firm of Mariani & Associates has been housed comfortably in Villa Pax, a striking 1887-built mansion at 1600 20th St. NW. Located opposite the Dupont Circle Metro station, the house "was going begging when I bought it," Ted Mariani recalled. The mansion is identifiable by its terra cotta dragons and copper gutters adorning its red brick facade.

Washington area purchasers of home building sites at Sugarmill Woods near Homosassa Springs on Florida's west coast are generally 45 to 60 and planning retirement two to 15 years up the line, according to Richard Erdman, manager of the Punta Gorda Isles office in Falls Church.He said he urges all prospective buyers to visit the 15,000-acre development site that is 62 miles from the Tampa airport. . . . Bearded Edmund C. Flynn, a condo-co-op specialist whose hobby is shooting crows on the Eastern Shore, is excited about the prospects of marketing a group of medium-rise condominium apartments to be built by Steve Middleman in Reston. Flynn said that the center elevator will provide nearly private, fan-out entries to all units in square buildings.

Among the unusual features of the new Madison of McLean town houses are the two-car garages in back. And the garages are separated from the houses by walled but open courtyards. The first section is sold out. A model furnished by Bloomies is expected to be ready early in June. . . . A move is under way in the Senate to raise the limit on FHA mortgages from $60,000 to $75,000. And the Senate banking committee has approved legislation that would reduce down payments and low initial monthly payments under the FHA graduated payment mortgage program.

George H. Bergdoll, vice president and regional manager of the H.G. Smithy Co. office in Norfolk, has told the Virginia Association of Housing and Community Development that lower rents for tenants with modes incomes can be possible by using now-controversial tax-exempt bond financing involving local redevelopment and housing authorities. . . . An apartment building at 1736 Columbia Road NW was sold recently for $425,000 by G.J. Quinn, trustee, to the Beverly Court Cooperative.

Eve Hertz, a realtor in Westport, Conn., heads a relatively new relocation service considers the lifestyle of the corporate wife as well as the executive.Phone: (203) 226-7801. . . . Housing magazine, a trade publication, reports that the soon-to-be-opened Colony Park apartments in Columbus, Ohio, will be a totally planned community for deaf persons. Lights will be used to announce arrival of guests. The 106-unit project will also feature vibrating beds that can be set to awaken residents in the morning.