The National Small Business Association, a private trade association representing some 50,000 small business in America, has bought a four-story brick building at 1604 K St. NW. The price, as reported by broker James L. Dixon, was approximately $550,000. The seller was Pacific Development Corp., with which the name of embattled Korean businessman lobbyist Tongsun Park has been associated. The trade association previously leased space at 1225 19th St. NW.

Transfer records show that former White House counsel Philip W.-Buchen and his wife have purchased a condominium residence at 800 25th St. NW in Foggy Bottom for $176,000. The seller was Inres Real Estate Corp.

At Rosenfeld Realty, a firm that specializes in shopping center development, leasing and management, founder Harry Rosenfeld is now 80 and a tenant counsellor. Son Samuel J. is running the business at 7101 Wisconsin Ave. NW. Granddaughter Frances A., 27, whose college credits include graduate work at Cornell and Harvard, has been on board for two years as director of leasing. She recently headed an idea exchange program held by the International Council of Shopping Centers.

A parking structure at 1575 I St. NW was sold recently for $2.6 million by Southern Regional Industrial Realty to 1575 I Street Associates Limited Partnership, a group for which developer Oliver T. Carr plans to erect a new associations office building in partnership with the American Society of Association Executives. The project, just west of the United Mine Workers headquarters at the northwest corner of 15th and I NW, will be started this year.

Appraiser Alfred Jarchow of Rockville discerned "only a slight upward creep" in the prices of existing homes sold in November in Montgomery County. He noted that the price level was moderated by a larger-than-usual proportion of town house and condominium sales with smaller average prices than detached houses. The median price of existing houses sold in November was $61,000. Total resales dropped slightly below the October volume but were about 10 per cent higher than in November, 197. Several area builders reported recently that sales of new dwellings were higher than usual in November and December.

If you are interested in a heavily documented Commerce Department study called Social Indicators 1976, it's available for $7 (check or money order) from the Superintendent of Documents, Government Printing Office, D.C. 20402. The detailed study of population and living statistics, including a section on housing demand and characteristics, shows, among many other things, that the total U.S. housing demand is expected to hold fairly level through 1981, show a slight downturn in 1991 and move up again in in the year 2000. CAPTION: Picture, Under[WORD ILLEGIBLE] Hyman Construction Co. has started the condominium apartment [WORD ILLEGIBLE] its Westbridge development at 29th Street and Pennsylvania Avenue, NW. The 11-story apartment building will adjoin an office building being complied at 26th and M streets. The Westbridge project will eventually, cover 100 acres between Washington Circle and Georgetown.