THE AMERICAN Association for the Advancement of Science has grown out of its longtime headquarters on Massachusetts Avenue and is vacating the distinguished free-standing building in favor of larger quarters on H Street NW.

Eventually, the association will sell the smaller building, which has served as association headquarters since it was built in the mid-1950s, said Edward I. Geisinger of Julien J. Studley Inc., broker in the transaction. The 25,000-square-foot building is one of the few free-standing buildings of its size in Washington, perched on an island of land between Massachusetts Avenue and Scott Circle at 15th Street NW.

The AAAS will move in May to 92,000 square feet of rented space at 1333 H St. NW, a large, new building, said J. Thomas Ratchford, associate executive of the association. He said AAAS initially considered buying a new building but decided to rent downtown because ample new office space in that area has resulted in rents that are lower than the association anticipated.

"We found the rents quite reasonable for the large amount of space we were looking for," said Ratchford, who declined to say how much rent the association will pay for its new office space. He said AAAS signed a 20-year lease for the space.

The AAAS, which has a membership of 136,000 scientists and a staff of 250, publishes Science and Science '84 magazines.

Besides the Massachusetts Avenue headquarters, the association currently rents office space in three other buildings in the downtown area.

"It was obviously time for them to consolidate into a building that was large enough to accommodate them," said Geisinger, who added that the new H Street building has a total 270,000 square feet of space. "They simply grew out of the old building years ago and have been renting pockets of space around town since then."

Geisinger, who helped handle the real estate transaction, said the Massachusetts Avenue headquarters is one of those unique buildings in Washington that surface in the market full of pluses and minuses. It is a free-standing building with windows on all sides and is set in its own garden. On the other hand it is small, and zoning regulations make it useful only to professionals and nonprofit organizations.

He said the building, assessed at $1.8 million, does not have a historical designation and could, conceivably, be torn down and a larger one constructed.

"There is no reason to do that, though," he said. "It's a lovely building in size with the lot. It's perfect for another association, one that's a little smaller in size, or for a law firm." PERSONNEL FILE . . .

The Northern Virginia Board of Realtors has elected Thomas M. Stevens its president for 1985. He is vice president and Virginia regional manager for Shannon & Luchs Co. and is president of the Washington Area Real Estate Council, publisher of Realtor magazine. He will be installed in December . . . Fred L. McKee has been elected president of the Maryland Association of Realtors. He is a member of the Prince George's County Board of Realtors and president of Fred L. McKee Realty Inc. The association also has named Vernon C. Terry, president of Terry's Realty of Havre de Grace, as its 1984 Realtor of the Year . . . David F. Seiders, formerly senior economist for the Federal Reserve Board, has joined the Naitonal Association of Home Builders as senior staff vice president of housing policy and mortgage finance . . . The Oliver T. Carr Co. has named Herbert A. Palm director of suburban properties and A. Joseph O'Brien senior leasing representative for all suburban properties . . . Smithy Braedon Co. has named Carolyn Davis assistant vice president and director of retail leasing . . . The Construction Management Association of America has elected Lee R. McClure, president of Construction Control Systems Inc. of Columbia, S.C., its new president . . . James A. Welu has joined Grady Management Inc. as vice president, development . . . Michael S. Brenner has joined Spaulding & Slye as property manager . . . James Wm. Moore, of Mead Associates in Lexington, Va., has been elected 1985 president of the Virginia chapter of the Farm and Land Institute of the National Association of Realtors. IN THE BUSINESS . . .

The Washington Board of Realtors Political Action Committee has voted to support four candidates for the D.C. City Council in the upcoming election. They are H. R. Crawford, Charlene Drew Jarvis, Carol Schwartz and John Wilson . . . A new Century 21 affiliate has opened in the area: Century 21 Advantage in Camp Springs . . . Hunter Development Co.'s 236-acre Little Rocky Run project on Braddock Road in Centreville has opened for sales. Some 1,100 homes are planned there, and Hunter is presently acquiring land and conducting feasibility studies for a second, 1,300-home phase . . . BMK Inc., headed by Bruce Davis, has begun selling town houses at its Hickory Ridge development in Waldorf. Some About 230 units, priced from $86,000, are planned for the 60-acre site priced from $86,000 . . . Henry A. Long Co.'s 73,000-square-foot Pender Mill I office building at Route 50 and I-66 will be ready for occupancy next month . . . Rouse & Associates has topped off its nine-story, 197,000-square-foot building at 8280 Greensboro Dr. in Tysons Corner. Occupancy is scheduled for early next year.