Virginia agriculture officials expect to begin aerial and ground spraying in isolated parts of Fairfax and Loudoun counties next week in an attempt to control the spread of leaf-eating gypsy moths.

The gypsy moth, which devastated 13.1 million acres of forest in the Northeast last year, is most dangerous in its caterpillar stage, which hatches in late April or early May, agricultural officials said.

Egg masses laid by female gypsy moths can contain 200 to 1,000 eggs; when the caterpillars hatch they feed voraciously on newly formed leaves, usually at night. Repeated defoliations can kill some trees and weaken others, making them more vulnerable to attacks by other pests and borers.

"We want to get a start on controlling these pests in Virginia instead of waiting until it's too late," said Robert Bailey, an assistant supervisor in the plant and pest control section of the Virginia Department of Agriculture and Consumer Services.

Egg masses that produce the gypsy moth caterpillar have been found in six locations in Fairfax County, one spot in both Loudoun and Fauquier counties and in the southern counties of Lunenburg and Floyd.

No egg masses have been found yet in Arlington or Alexandria, Bailey said, "but it is a general assumption that Northern Virginia is next in line as far as the general southward spread from the northeastern states is concerned. We also presume there are other infected sites in Northern Virginia, but we haven't found them yet."

The gypsy moth spreads naturally with the aid of wind, and artificially with the aid of people. The female, which does not fly, crawls into cracks on outdoor objects such as trees, wood piles and window ledges and under the eaves of houses to lay her eggs. She also hitchhikes on recreational vehicles, tents, mobile homes and hauling-trailers--which is how state agriculture officials suspect many of the moths migrated here from the Northeast. Recreational vehicles are more suspect because they often are parked for several days in woody areas or campsites that may be infested.

State Agricultural Commissioner Mason Carbaugh said a half-mile radius surrounding the infested areas already discovered in Northern Virginia will be quarantined later this summer, provided various oversight committees of the state legislature do not object.

Once in effect, Carbaugh said, the quarantines would allow state inspectors to block infested shipments of agricultural products such as firewood from leaving the restricted areas and to require inspection of recreational vehicles leaving the areas. Violation of the quarantine would constitute a misdemeanor.

Some areas will be treated next week, weather permitting, with chemicals sanctioned by the U.S. Environmental Protection Agency as safe for humans, pets and plant life. The chemicals to be sprayed are Thuricide, Dimilin and Dylox, none of which has long-term residual effects, agriculture officials said.

Aerial spraying will take place next Tuesday for 65 acres in the Loudoun County town of Lucketts, 50 acres in the Southdown subdivison in Great Falls and 33 acres in Springfield. A two-acre section in the Annandale Acres subdivision is scheduled for ground-spraying late next week or early the following week.

In other areas, officials will lay chemically treated traps to attract and confuse male gypsy moths and disrupt breeding.

Egg masses found on a tree on Auburn Street in Annandale, on a tree on Red Spruce Road in Fairfax City and on a tree in West Park, an industrial park in McLean near Tysons Corner have been destroyed and traps will be set to monitor any further infestation, agricultural officials said.

Residents living in the areas to be sprayed already have been notified, officials said, and will be reminded again before the spraying starts.

"We've advised them to stay indoors and get their pets and any laundry indoors," said Ralph Donnell, Fairfax County's gypsy moth control supervisor. "It's not that they have to, but it just makes common sense not to stand outside while a helicopter is spraying overhead."

The privately owned helicopters hired for the job are expected to start spraying the Great Falls section at 7 a.m. and the Springfield area around 9:15 a.m., officials said. They said those times were picked because minimum activity would be expected outside--too early for school children to be out, they said, and late enough that most adults would have gone to work.

The spray should dry within 20 minutes to an hour after it is applied, they said.

The Fairfax County Board of Supervisors has appropriated $35,000 to help combat the gypsy moths, which are particularly fond of the oak and hickory trees that make up more than 78 percent of the county's forest area.