IN THE BUSINESS . . . Housing is getting steadily more affordable, according to calculations by the National Association of Realtors, which tracks the relationship between the median family income and the median house price to compute an "affordability index." The Realtors take the median house price, look at prevailing interest rates, and then figure out what income would be required to qualify for a loan. This index rose to 80.4 in February, meaning that the U.S. median family income was 80.4 percent of what would be required to qualify to buy the median house, now priced at $68,300. This marked the ninth straight month of improvement -- the low was 65.2 last May -- but far from the good old days of the late '70s, when the index topped 120 . . . Not unrelated is the news that sales of existing homes hit an annualized rate of 2.47 million units in February, up 24.1 percent from a year ago. Though the rate was down slightly from January, experts in the field were pleased with the numbers. "The encouraging news is that, after the strong surge in January, the February sales level remained healthy," said Jack Carlson, the NAR's chief economist . . . Locally, the signs are even better, according to William Garretson, senior economist at New York's Citibank, who spoke to the Northern Virginia Board of Realtors last week. Garretson forecasts housing starts in the Washington area this year "equal to 1977's 25,000 peak. They could go higher in 1984, to provide the best real estate market the area has seen since the early 1970s" . . . The Salesman's Council of the Washington Board of Realtors honored the 1982 members of the Million Dollar Sales and Listing Club at a luncheon Wednesday. . . . The D.C. Housing Industry Corp. had its annual community development awards dinner Thursday. Honored were Asbury Dwellings Inc., the General Scott, the Heights, McCollough Paradise Gardens, Shiloh Family Life Center, and Wah Luck House. The keynote speaker was R. Robert Linowes. For information, call Sally Meyers at 628-4494.

PERSONNEL FILE . . . The Federal National Mortgage Association has named Richard H. Daniel its vice president for marketing. Daniel has been with Wells Fargo & Co., where he was vice president and manager of the real estate division of the Retail Banking Group . . . William H. Knott, president of William H. Knott Inc. of Lutherville, Md., has been elected president of the Baltimore-Washington chapter of the Metal Building Dealers Association. . . . Mary Gray has joined Manarin and Odle Realtors Inc. as an agent in the firm's Old Town Alexandria office . . . Coldwell Banker Routh Robbins Realtors Inc. has named Carole Porter sales manager of its Mount Vernon office . . . Thomas J. Long has joined the sales staff of Casey, Miller, Kornblatt & Burns, Inc., commercial and industrial Realtors.

ON THE MOVE . . . The Mozel Development Corp. of Vienna announces that its Tyson's Interchange Building at Tyson's Corner will be ready for occupancy this spring. The $40 million, eight-story building has about 275,000 square feet of office and retail space and underground parking for 600 cars . . . Richard Shea of DeRand Realty Corp. of Arlington announces the sale of the Crestview garden apartments in the Landmark section of Alexandria to Whiting Street Associates. The complex -- 25 two-story buildings on 8 1/2 acres, 291 units in all -- is expected to remain rental, and Shea says the new owners will upgrade the property substantially . . . Glen J. Koepenick Inc., a commercial real estate brokerage based in Rockville, has merged with HBW Realty Inc., and its president, Glen J. Koepenick Jr., will join HBW as executive vice president