The median adjusted gross income of married couples who filed income tax returns in Virginia in 1979 was $19,752, a 9.6 percent increase over 1978, and couples in Northern Virginia had the highest median income for all of Virginia, according to a report by University of Virginia's Tayloe Murphy Institute.

Despite the increase, income figures actually declined 1.5 percent in the face of an inflation rate of 11.3 percent for 1979.

In Northern Virginia the top five localities were Fairfax County ($32,429, an increase of $1,776); Fairfax City ($29,260, a $2,265 increase); Arlington County ($27,947, up $1,630); Alexandria ($26,112, an increase of $2,393) and Prince William County ($25,937, a $2,222 rise).

The Northern Virginia portion of the Washington, D.C., Virginia, Maryland Standard Statistical Metropolitan Area had a median income of $29,458, followed by Richmond with $22,277. The lowest median was in the Virginia portion of the Johnson City-Kingsport-Bristol SMSA ($14,314).

The report found that 3.6 percent of married couples had adjusted gross incomes of $3,000 or less, and 10.3 percent made $40,000 or more. Fairfax County had the greatest number of high incomes, with 32.2 percent of returns from couples making $40,000 or more.

The adjusted gross income for individuals filing returns in Virginia was $6,923, a 6.9 percent increase over 1978, but a 4 percent decline after adjusting for inflation. Arlington County had the highest median individual income -- $11,736, and Northampton County had the lowest -- $4,416.