A small but persistent taxpayers' organization in Fairfax County has long complained that commercial and industrial properties are taxed too lightly by the county.

In response, the county has produced a number of statistics that County Executive Leonard L. Whorton says show that "Fairfax County has one of the most uniform and equitable property assessment records in the United States." The report was compiled by county staff members at the request of the board of supervisors.

One of the indicators used by the county is the sales-assessment ratio. The accuracy of the assessment is presented as a percentage of sales price - 100 per cent being perfect.

In 1976, the overall sales-assessment ratio in Fairfax was 88 per cent. The 15,880 properties that changed hands in 1976 sold for a total of $1,017,343,657. They had been assessed at $890,084,645.

According to county figures, the sales-assessment ratio of commercial and industrial properties and apartments in 1976 was higher - 91 per cent. The 1,574 sales of these properties totaled $86,322,321. The assessments on the properties totaled $78,361,615.

Figures going back to 1971 showed a consistent trend of higher sales-assessment ratios for nonresidential properties.

Some other figures, while not reflecting on the county's fairness in assessing different kinds of properties, seem to offer clues as to why some homeowners grumble - especially those in the Fairfax County Taxpayers Alliance.

Between 1974 and 1977, the average value of commercial and industrial properties increased by only 22.1 per cent, while the average value of residential properties increased by 29.2 per cent.

Samuel J. Patteson, the county's veteran assessments director, said the difference was a reflection of the market. In other words, houses were more popular with buyers than apartments or other commercial and industrial properties.

The supervisors voted unanimously to adopt the staff presentation, given at their meeting this week. Supervisor Audrey Moore (D-Annandale), who in the past has criticized the county's assessments of commerical and industrial properties as too low, also supported the document.

In other action this week, the supervisors approved promotions for two veteran county officials - Mary Elizabeth Holbein to director of the office of research and statistics and Shiva K. Pant to director of the newly created office of transportation.

Holbein, 32, is currently managing the county's community development program aimed at rehabilitating deteriorating neighborhoods. As director of ORS, at a salary of $31,091, she will head a department that has assumed an increasingly important role in planning growth.

Pant, 31, is now chief transportation planner in the office of comprehensive planning.