New construction activity in metropolitan Washington increased significantly last year, spurred on by a sharp upturn within the District, according to final figures for 1976 published by the Commerce Department.

The value of construction permits approved by all area governments last year was $1.25 billion, up $258 million or 26 per cent from 1975. Non-residential office, commercial and industrial buildings accounted for about half the total.

Housing construction was responsible for most of last year's gains with 17,509 new housing units started, and increase of 7,688 or 78 per cent from the postwar low during previous year and slightly ahead of the 16,887 total in 1974.

Both 1975 and 1974 were unusually depressed in the housing industry, with new construction blocked by sewer moratoria and high interest rates for mortgages. The metropolitan area recorded 37,402 housing starts in 1973 the last boom year here.

According to the Metropolitan Washington Council of Governments and private industry data, areawide housing starts in January slumped to about 1,000 units - the lowest monthly total since February 1976 - partially because of bitter cold weather.

In the District last year, 2,199 housing units were authorized, or five times the 1975 total. Although most new housing construction in the city was for apartment units, single-family housing accounted for some three-fourths of all area starts last year.

More than half the new housing units authorized last year are in Northern Virginia, with 5,724 in Fairfax County alone. Housing starts in Montgomery and Prince George's countries totaled more than 5,000 a gain of 63 per cent over 1975.

In terms of total value for all construction, Northern Virginia permits totaled $506 million, a gain of 28 per cent; Maryland permits were $456 million, up 3 per cent; and D.C. permits totaled $291 million, up 83 per cent.

The $1.2 billion in new construction last year was the highest since 1973, when $1.37 billion of permits were approved in the metropolitan area.

Only Prince George's and Arlington Counties experienced a slowdown in new construction approved last year. In Prince George's the value of new permits was off 37.5 per cent to $149 million while in Arlington, new permits totaled $33 million, down 38 per cent from 1975.