The office vacancy rate in the District's downtown business center has risen to about 4 percent recently from less than 0.5 percent in January, according to an official of the Braedon Companies.

The increase represents a softening in space absorption that is less severe than the decline previously forecast by some industry anaylysts, said James L. Eichberg, president of the Washington-based commercial leasing and management company.

Eichberg based his assessment on current local data and a 17-city survey based on earlier statistics released yesterday by Office Network Inc., a consortium of real estate companies headquartered in Houston. Braedon is an affiliate of ONI.

Washington and Los Angeles each posted a central business district vacancy rate of .4 percent on Jan. 15, the lowest of all the cities surveyed; Atlanta's 16.1 percent rate was the highest. Washington also had the lowest vacancy rate for total commercial space of 1.7 percent.

The central district vacancy rates for other cities in the survey were: Baltimore, 3.5 percent; Boston, 3.5 percent; Chicago, 3.2 percent; Dallas, 4.3 percent; Denver, 1.6 percent; Hartford, 9.1 percent; Houston, 2.1 percent; Kansas City, Mo., 1.9 percent; Miami, 5.1 percent; New Orleans, 3.5 percent; New York, 4.1 percent; Philadelphia, 5.2 percent; Pittsburgh, 1.7 percent, and San Francisco, 4.2 percent.

The District's current 4 percent rate compares with a 4.1 national average based on the survey's January statistics, Eichberg said.

Washington ranked seventh in construction activity, ONI reported, with 11.6 million square feet under construction. Houston took the top spot with 28.4 million square feet; Kansas City was low with less than 1 million square feet.

ONI surveys are conducted twice a year. Copies of the current office market report can be obtained by writing the Braedon Companies, 1150 17th St. NW, Washington, D.C. 20036.

Other developments in real estate in the Washington area:

* Union Oil Co. of California has leased over 25,000 square feet at 1050 Connecticut Ave. NW.

* Attorneys Office Management Inc., has signed a 25-year lease on 71,583 square feet at 1275 K St. NW.

* Housley, Goldberg and Kantarian, a law firm, has leased over 13,000 square feet at 2301 M St. NW.

* Quarles & Brady, a law firm, has leased 3,000 square feet at 1300 19th St. NW.

* McClure-Lundberg Associates, a management consulting firm, has leased 3,700 square feet at 1515 U St. NW.

* The Synectics Group Inc., a consulting firm, has leased over 4,000 square feet at 1130 17th St. NW.