When California began its widespread aerial assault on the Medfly last year, many environmentalists and homeowners protested bitterly. Virginia begins a similar but more limited assault on gypsy moths in Fairfax County today, with nary a complaint yet logged.

One reason: Killing off the Mediterranean fruit fly, now apparently eradicated in California, required a potent and controversial insecticide, malathion. But eliminating the eggs of the gypsy moth will be done with an organic spray called Bacillus thuriengiensis, commonly known as "B.t.," which officials say is not dangerous to people or animals.

That said, Fairfax County officials urged residents of today's two target areas to remain indoors when the state-owned chopper is overhead. The two areas slated for spraying are a region along Jefferson Run Road in Great Falls, starting about 7 a.m., and an area along Gambrill Road in Springfield, starting about 9 a.m.

About a dozen homes are affected in each area, and county police will keep other traffic out while the low-flying helicopter is at work.

Aerial spraying represents an escalation from prior ground-level spraying. Gypsy moth egg masses have been reported this spring in the Annandale, Springfield, McLean, Great Falls and Fairfax City areas.

Gypsy moth caterpillars devour young leaves of hardwood trees so quickly and thoroughly that, if repeated in successive years, the trees cannot recover.