SOME 5,529 PROPERTIES valued at $343 million changed hands in Baltimore during the first half of the year, according to information compiled by Rufus S. Lusk & Son. That worked out to an average sale price of $62,000, Lusk said.

The biggest transaction was the sale of the Baltimore Hilton Hotel by Abruzzi N.V. to HMK Limited Partnership for $35.6 million.

Seller take-backs were the largest single source of financing, Lusk found, with 423 first trusts totaling $23 million, and Maryland National Mortgage led institutional lenders with 331 loans for $13.6 million. A total of 4,255 first mortgages worth $291.3 million were written during the period. These included 782 FHA and 128 VA loans.

MONTGOMERY COUNTY is reducing its transfer tax on some home sales, the county Board of Realtors notes.

A new county law, effective Thursday, changes the tax brackets into which various sales prices fall. Current law imposes no tax on improved residential property sold for less than $25,000, 0.25 percent on property priced $25,000 to $35,000, and 1 percent on property priced over $35,000.

Under the new law, sales up to $40,000 will be taxed at 0.25 percent, $40,000 to $70,000 at 0.5 percent, and over $70,000 at 1 percent.

While the new law subjects properties under $25,000 to tax for the first time, there so few of those that the chief practical effect will be to halve the tax on homes in the $40,000 to $70,000 range.

PERSONNEL FILE . . . The Washington Board of Realtors has chosen Lillian E. Bowen of Weaver Bros. Inc. its 1984 Realtor of the Year. The board also has named E. Brooke Lee Jr. of Merrill Lynch Realty Realtor-Associate of the Year. John W. Gill, of H. A. Gill & Son, will receive the Martin I. Isen Award for public service; Brian W. Ball, of Shannon & Luchs Co., will receive the Donald C. Rosinski Award for commercial leasing, and a special award of appreciation will go to James G. Banks, the board's former executive vice president. The awards will be presented at the board's annual dinner dance Oct. 20 . . . Dale L. Ross, president of Pioneer Realty Inc. and Marydale Realty Management Inc., has been sworn in as the Montgomery County Board of Realtors' 1984-85 president. And the board has chosen Faye D. Cobb, of District-Maryland Realty Inc., as its Realtor of the Year. Also installed as officers were Harvey Rosendorf, of Harvey Rosendorf Inc. Realtors, president-elect; William Ellis, of Shannon & Luchs, vice president; Elaine White, of Long & Foster Inc., treasurer, and Betsy Abruzzo, of Lewis & Silverman, secretary . . . Michael D. Fox, president of Realty World-Fox Realty, has won the Virginia Association of Realtors' Realtor Code of Ethics Award. The association also named John A. Stookey, of Long & Foster, Salesman of the Year . . . Centennial Development Corp. has named David L. Smith executive vice president and chief operating officer . . . The Donohoe Cos. have promoted James M. Kernan to vice president of John F. Donohoe & Sons, Realtors . . . Otis Warren Jr., of Otis Warren & Co. Inc., Baltimore, has been elected to the board of directors of the Enterprise Development Co. . . . Jackie Dorfman has been appointed director of residential sales at Randall H. Hagner & Co. . . . Cassidy, Jaeger & Pinkard Inc. has appointed Blane T. Dodson a vice president.

IN THE BUSINESS . . . The National Association of Home Builders recently honored the Northern Virginia Builders Association for its efforts at "developing programs to combat excessive regulations that increase the cost of housing . . . The Community Associations Institute will hold its national conference Oct. 25-29 in Philadelphia. For information, call 548-8600 . . . The Capitol Hill Brokers Council is sponsoring a session for agents and brokers Wednesday with Mayor Barry's staff concerning development around Union Station and on H Street NE. For information, call 544-7714 . . . James R. Hunter, former senior vice president of commercial leasing at Smithy Braedon Cos., has established his own commercial brokerage, leasing and consulting firm, Hunter & Associates, with offices at 2000 Pennsylvania Ave. NW . . . Lee Sammis Associates Inc. has formed an investments division to acquire improved properties in this area. The firm is looking for projects and buildings of 100,000 square feet and up . . . On the commercial construction and development front: The George Hyman Construction Co. has begun work at 1001 Pennsylvania Ave. NW on the 435,000-square-foot first phase of Cadillac Fairview Urban Development and Lehndorff & Babson Real Estate Counsel Inc.'s project there; Omni Construction Inc., has started work on 2750 Prosperity Ave. in Fairfax, a 118,000-square-foot building developed and owned by Prudential Insurance Co. of America; Donohoe Construction Co. has begun construction on a 33,000-square-foot, six-level office building, owned by J. Patrick Blew, at 1015 31st St. NW; Phase Two of the Parkridge Business Center in Reston, a 100,000-square-foot, two-story building, is under way. Developed by Walker and Co., the project was designed and master planned by the architecture firm of ADD Inc.; construction is nearing completion on Centre Pointe I, a 144,000-square-foot office and R&D project on the Beltway in Landover. It is being developed for Wachovia Bank and Trust by Birtcher/Butcher; more than 80 percent of the Gaithersburg Office Center, a 10-unit town-house project, has been leased. The center offers office suites as small as 355 square feet, with rents on the remaining units beginning at $11 a square foot plus utilities. Leasing is by HBW Associates.

ON THE MOVE . . . The National Housing Partnership has leased 153,000 square feet at 1225 I St. NW for its new corporate headquarters. The 200,000-square-foot building, being developed by the John Akridge Co., is 75 percent leased and is scheduled for completion in spring of 1986. Smithy Braedon represented the tenant; the John Akridge Co. represented the landlord, 1225 Eye St. NW Limited Partnership . . . Studioline Corp. of America, a producer of commercial-free high-fidelity music transmitted by satellite, has leased 14,200 square feet at Executive II of Centennial Development Corp.'s Commerce Executive Park in Reston.