The Washington metropolitan area led the nation in new office construction during the first six months of this year, according to a recent study.

Of the 117 million square feet of office space under construction during the first half of 1987 in the 32 U.S. cities surveyed, Washington captured nearly 16 percent of the total market, according to Smithy Braedon, a local real estate company that prepared the report. The study was published by the Office Network, a national alliance of commercial real estate firms.

During the first six months of 1987, a total of 18.1 million square feet of office space was under construction in the Washington area. The local area ranked second in new office space rented with nearly 5 million square feet. Chicago led all surveyed cities in new office office space rented.

Manhattan, with 226 million square feet, was still ranked as the world's largest office market by the survey, which covered 42 cities in the United States and overseas. Manhattan was followed in total office space by Chicago, London, Los Angeles, Houston and Washington.

Midtown Manhattan's office rental rates average $40 per square foot annually, making it the nation's most expensive office district. That is more than double the national average.

Boston ranked second in office rental costs at $33 per square foot, followed by Los Angeles and Washington at $32 each.

Houston, still suffering from the oil bust, had the largest amount of vacant office space, 48 million square feet, and the highest vacancy rate, 32 percent.

Manhattan, at 11.3 percent, had the lowest vacancy rate. Munich's 1.2 percent vacancy figure was the lowest internationally.

The overall U.S. office vacancy rate during the first six months of this year was 19.3 percent, up 7 percent from the last half of 1986, the report said.

In a related report released this week, the Washington area's vacancy rate stood at 13.4 percent for the third quarter of this year.

That figure is up from 12.9 percent in the previous quarter, mostly as a result of the recent completion of more than 5 million square feet of new office space, according to Spaulding & Slye, a local real estate investment firm.

During the most recent quarter, the vacancy rate in the District was 9.2 percent, down from the second-quarter rate of 11.5 percent.

Suburban Maryland vacancy figures increased from 12 percent to 15.7 percent, and Northern Virginia's rate went from 15 percent to 17 percent.

Arlington County's office vacancy rate, which over the past decade has hovered around 7 percent, jumped to 16.2 percent during the third quarter.

The report blamed the figure on high vacancies in Crystal City and the area around the Ballston Metro station.

One of the largest real estate transactions in Frederick County was recently completed with the $8 million sale of more than 420 prime acres in Ijamsville, four miles east of Frederick.

The property was purchased by Ann Grimm, a partner with Gary P. Grimm Inc., a McLean residential and commercial development firm, according to Long & Foster Realtors and the Maryland Real Estate Group, two companies involved in the sale.

The land, sold by M. Robert Ritchie, includes about 270 acres of farmland and the 150-acre Holly Hills Golf Course. Ritchie built the golf course in 1977 after having farmed the land for nearly 40 years.

The new owners expect to develop the property into a residential complex of more than 220 luxury homes, with 80 percent of the houses surrounding the golf course.

Three former executives of two Washington area companies have formed RBA Development Co.

Ronald Bruck, William Sargis and Andrew Jones have created the commercial real estate firm to focus initially on developing warehouse and research and development office buildings in Virginia and Maryland.

Bruck, formerly an executive vice president of the Alan I. Kay Cos., will be in charge of site acquisition, finance and marketing for the new firm.

He is also president of the D.C. Building Industry Association and a member of the Metropolitan Washington Builders Council.

Sargis, formerly president of Sargis & Jones, will be responsible for the company's interior project management and general contracting activity.

Jones, who was executive vice president of Sargis & Jones, will handle RBA's management, consulting and computer systems.

The D.C. Court of Appeals has ruled that George Washington University will not be allowed to construct an addition to a medical building.

The court reversed the decision in Draude v. D.C. Board of Zoning Adjustment, in which the board had granted the university two variances and two special exceptions to expand its H.B. Burns Memorial Building.

In challenging the board's approvals, James Draude, who lives in the President Condominium, accused the board of making several errors in approving the plan.

For example, Draude said that GWU failed to get a proper variance for the expansion of a nonconforming structure and that the board did not justify its decision to grant a special exception. Sales of existing homes nationwide declined in August, continuing a trend that was brought on by an increase in mortgage interest rates, the National Association of Realtors reported.

The August sales figures showed a seasonally adjusted resale rate of 3.4 million, down nearly a full percentage point from July, according to the NAR.

"Last month's decline in home sales is a reflection of interest rates, which have been drifting up since early last spring," said John A. Tuccillo, the chief economist of the group.

"More people were forced to buy less expensive houses, or to abandon their purchase altogether," Tuccillo added.