The value of contracts for future construction in the District declined by 6 percent -- from $304.3 million to $250.3 milliion -- in June from a year earlier, the F. W. Dodge Division of McGraw-Hill Information Systems Co. reported this week. Most of this decline was in nonresidential construction, the company said. The year-to-date total was down 18 percent.

Open University of Washington is offering a one-night class in how to buy a condominium next Tuesday and one on how to buy a house Aug. 18. Both cost $10. For information on location and registration, call 966-9606.

The Department of Housing and Urban Development has awarded 19 grants totaling nearly $200,000 to architects, builders, universities and associations to stimulate the use of innovative, low-cost home building. Among the award winners was Rural America, a Washington-based organization. a

The Rouse Co. of Columbia said it plans to sell its rental apartments at The Village of Cross Keys in Baltimore to Shelter Corp. of Canada, Ltd. The Canadian company already owns more than 5,000 apartments in Columbia and Echelon, N.J.

A free catalogue of new real estate books is available to "all members of the real estate profession," the Prentice-Hall publishing company announced. Requests should be sent to Joseph Schaumburger, Prentice-Hall, Englewood Cliffs, N.J. 07632. Ask for Book News Catalogue No. 8 and enclose a stamped, self-addressed envelope.

The Landmark Office Building on South Whiting Street in Alexandria has been sold by Bruce and Betty Stauffer for $2.75 million to the Bader Tenants Association, who traded it to the Howar Trust for the Badar Apartments, which was valued at more than $2 million, Weaver Bros., Inc., reported.

A passive-solar and earth-sheltered house, built in part with an experimental grant from the Department of Housing and Urban Development, will be open today and tomorrow from 10 a.m. to 4 p.m. in the Whiting's Neck community near Shepherdstown, W. Va. Designed and built by Randall B. Ashelman, of Natural Sun Homes, the house is located on five acres overlooking the Potomac. It is for sale for $149,000. For information, call 304-263-6616.