Fairfax County, which has courted business aggressively with flashy advertising and glittery New York luncheon presentations, experienced record growth in the number of new firms, occupied business space and jobs created in the past two years.

According to a new county directory released last week, the number of new firms that have moved to Fairfax has increased by 20 percent since 1979, occupancy of building space has grown by 38 percent and jobs have increased by 28 percent.

The county report covered only basic industrial and industrial service firms and not retail firms, government offices, real estate agencies, medical and legal services or financial institutions. Industrial-related firms represent about one-fourth of the county's 250,000 jobs, county officials said.

The report "is really telling us two things," said James W. Todd, vice chairman of the Fairfax County Economic Development Authority. "First, in spite of a depressed economy, the county's business climate is very healthy. And second, as much as we like the success and publicity of attracting Mobil Oil, Tandem Computers, AT&T and other large corporate organizations from outside the county, the real story is the healthy expansion of the hundreds of firms already here," he said.

Particular increases in expansion came in the areas of research and technical manufacturing, high technology, national trade and professional associations, corporate headquarters and marketing offices, and transportation and warehousing firms.

During the past 10 years, the number of basic-industry firms rose from 615 to 1,690, an increase of 175 percent, the report said. Also during the decade, jobs increased by almost 5,000 annually, from 28,068 to 72,561, an increase of 159 percent.

Occupied building space also rose, from 9.3 million square feet to 24.2 million.