Led by the counties and cities of Northern Virginia, the state's unemployment rate fell one-half point in April to 3.4 percent, the lowest rate since last August and the lowest April rate in 17 years.

Although some pieces of evidence indicate that the Washington-area economy is slowing down, there was little sign of it in the Northern Virginia job figures released by the Virginia Employment Commission. Falls Church had the lowest jobless rate in the state: 1 percent. The rate for all of Northern Virginia was 1.6 percent, lower than any of the state's other urban areas.

Of the Northern Virginia jurisdictions, only Alexandria had a jobless rate higher than 2 percent; it was 2.1 percent.

The only sign of softness was in construction. The number of construction jobs in Northern Virginia was down 6,700 from April 1989, to 56,400. And the unemployment rates in several outlying counties -- Culpeper, Stafford and Orange, for instance -- were up a bit. Many construction workers live in these farther-out counties.

Overall, employment in Northern Virginia rose 15,900 compared with April 1989. For the state as a whole, employment was 2,918,700 in April, second only to a high of 2,919,000 jobs reached last November.

The figures are not adjusted for seasonal variations; the comparable U.S. unemployment rate for April was 5.2 percent.