Final statistics on area construction activity last year establish convincingly that Northern Virginia expansion currently is driving the local economy. But the date also show that Prince George's County is making the sort of leap that the Maryland county's leaders have been promoting.

Throughout metropolitan Washington, the value of all construction permits issued in 1979 was about $1.9 billion, up just $37 million (2 percent) from the previous year.

Of all the new construction, 55 percent or more than $1 billion was concentrated in the Northern Virginia suburbs. Fairfax County, with $699 million, led all area jurisdictions with a third of the metropolitran total and a gain of 12 percent over 1978.

Montogemery County was second overall at $329.9 million (up 3.7 percent) but the largest gains in total and relative value of new construction were in Prince George's at $254.8 million, up $83.2 million or 48.5 percent.

Other increases were recorded by Charles County (6.7 percent) and Arlington County (11.3 percent) while declines were registered in the District (34 percent, to $206 million from $312 million), Loudon County (32.4 percent) and Prince William County (6.4 percent).

The key factor in the lackluster construction activity overall was in the housing sector, where soaring interest rates led builders to postpone new projects. As a result, area housing starts authorized by permits fell 9.5 percent to 21,928 from 24,238 units, according to Commerce Department data.

The annual rate is far below the peak of 55,000 units a year registered here in the mid-1960s and far below what area economists say will be needed to meet demand for housing in the 1980s from new households. This is expected to lead to a crunch that will propel area house values upward once again.

In D.C., for example, where demand for smaller units is very strong, housing units authorized plummeted in 1979 to 1,652 from 2,676 in 1978. The only substantial increase was in Montgomery County, where permits rose to 4,944 from 4,301. Single-family house construction remained strong in Montgomery, accounting for the 1979 gain. Throughout the area, single-family units accounted for eight of ten new starts.

Nonresidential permits, for offices, commercial and industrial construction, totaled $756 million or 40 percent of all activity last year, up 4.3 percent from 1978. Again, Fairfax led the way with $257 million (mostly retain and offices), a gain of 14.4 percent.