After more than two years in planning and two more in reconstruction, the conversion of the 1836-vintage Green's Steam Furniture Works into 16 expensive condominium apartments has been completed at 200 South Fairfax Street in Old Town Alexandria. Remodeled for $1.5 million by Ellsworth-Howell Developers, the former factory (and more recently foreign car garage) now includes a striking, interior atrium and vari-shaped, one and two-bedroom apartments. All but one of the apartments have been sold. The remaining unit has two stories and an open arcade on the top level. Price: $179,500. Co-developer Sam Ellsworth said that contracts on the units were signed more than 18 months ago but that some buyers backed out when the restoration work took longer than anticipated. Michael & Michael were the architects and John W. Rust the project architect, W.R. Manchester Inc. was the general contractor.

Sales at Skyline House, a 16-story condominium building that won't be completed until next year, have been unusually strong, according to manager Gene Roberts. He said that 116 reservations were taken in two weeks at the Bailey's Cross roads project and that all of the 273 units, which are priced from $54,000 to $127,000, are expected to be sold before the end of the year. It is located at Skyline City, where the Charles E. Smith organization has also sold out two 16-story condominiums. It has two fully leased highrise apartment buildings and a new office building, with another that will be ready for occupancy in February.

SHORTLY: The National Association of Realtors reported that in Angust, existing houses sold at a rate of 4.08 million units, a seasonally adjusted annual rate. Only in December 1977 had the annual rate ever before exceed 4 million . . . Appraiser Alfred Jarchow's August study of resale prices in Montgomery County showed them 14 percent above the level of a year earlier . . . In Northern Virginia, realtor multiple listing statistics for September showed total residential sales of 1,753 units for $134 million, with an average price of nearly $77,000 . . . Bender Associates now is the owner of the former Neisner department store building on the southeast corner of 12th and G streets NW. It was a $1.8 million purchase. Morton Bender says there are no plans at present for the building.