The state of Maryland has arranged for a DC-3 to take a big swat at the thousands of mosquitoes that for the last month have plagued residents of the tiny Eastern Shore Communities of Chance, Deal Island, Dames Quarter and Monie.

The plane, state Agricultural Department officials said, is tenatively scheduled to spray more than 10,000 acres of farm and marshland near the Chesapeake Bay with insecticide sometime after dawn Wednesday.

Lt. Gov. Blair Lee II said yesterday the state had decided to finance the $10,000 aerial spraying effort because a new brood of mosquitoe is scheduled to move off the marshlands this week "and we thought we better get in and zap them."

The brood would be the third largest batch of mosquitoes to descend on the area, often in dark cloud-like swarms, since early April. The mosquito population is the largest charted anywhere in Maryland in 20 years, according to state Agriculture Department officials. It has caused so much annoyance that some local residents have put up their homes for sale.

Residents have lobbied for aerial spraying for three weeks, but Somerset County officials were reluctant to help finance it because they felt it would lead to spraying requests from other communities with mosquito problems.

Lee said the state agreed to sponsor the spraying "with the understanding that it would be a one-shot deal that would not set a precendent for other places."

The spray to be used is Malathion, an organic pesticide approved for use by the Environmental Protection Agency. It is commonly used in household gardens and has been found to be harmless to quail and fishlife in tests conducted by state Agriculture researchers, spokesmen said. It is a "contact" spray, which breaks up quickly in the environment and kills only adult mosquitoes, not larvae, spokesman said.

The original permit granted for the spraying excluded wetlands where most of the mosquitoes breed, but Lee and Agriculture Department officials yesterday indicated that the state Natural Resource Department will lift that ban.

The huge mosquito population apparently was caused by a combination of high tides, rain and warm weather in late March and early April. The tides flooded low marsh areas, and salt marsh mosquito eggs that were laid in the marsh soil last fall were hatched as a result.

How bad have the bugs been? "They're solid in the air everywhere," says Elsie Parks, postmistress at Chance.