Commercial office space leasing in Fairfax County has increased a little over 10 percent, according to a Fairfax County Economic Development Authority report. The report covers the eight-month period from August 1982 through March 1983.

The EDA reported an average of 183,000 square feet of space leased per month in the county during that period. The eight-month total was 1.47 million square feet. During the previous seven months, from January 1982 through July 1982, 166,000 square feet of space was leased per month. The total seven-month figure in 1982 was 1.16 million square feet.

Of the 1.47 million square feet leased during the latest period, more than 600,000 square feet was in recently completed buildings, while more than 300,000 square feet was in previously occupied space. The total also includes 396,000 square feet of pre-leased space under construction and 170,000 square feet of commercial space in the planning stage.

The Tysons Corner area leased the largest amount of space in the county, with 852,000 square feet. Both Reston and Fairfax Center, the area west of Fairfax City at the conversion of I-66 and U.S. Route 50, had strong leasing activity, with about 150,000 square feet leased in each area.

The Fairfax County Economic Development Authority report covers only commercial office space in the leasing market. Fully leased buildings, nonspeculative buildings-buildings "built-to-suit" and condominium and townhouse offices for sale are not included.

As of March 1983, Fairfax County contained more than 2.6 million square feet of commercial space available for leasing. This includes previously occupied space, recently completed projects and projects under construction, but does not include 8.3 million square feet of space in planned projects.

Other developments in commercial realty in the metropolitan area:

* Three leasing transactions have been completed at 4801 Massachusetts Ave. NW: Levy & Smith, a law firm, has leased about 3,500 square feet of space; Stanley E. Clark & Associates, a pension consulting firm, has leased 1,700 square feet, and Vogue Travel has leased about 1,100 square feet.