At first glance, Janice Bania thought they were bats, small black bats flapping and screeching across the sky.

But then, a closer look showed they were actually a band of blackbirds and starlings so thick that they looked like the belly of a giant whale floating in the sky.

"I thought Hitchcock was filming something," the Alexandria resident said. "I have never seen so many birds. They were in trees, in the sky. As far as you could see there were screeching birds."

Yesterday, after city officials began hearing stories similar to Bania's, Alexandria Health Department officials ordered 12-gauge shotguns and 16-mm pistols to uproot the birds from their roosts. At Tuesday night's City Council meeting, the officials discussed using a small cannon, with boom but no ball, to disperse the blackbirds and starlings, but then opted for the more conventional shotgun "bird bombs," projectiles that explode in midair.

Bania, who along with her 4-year-old son Justin first saw the flock Sunday, said it has reappeared each night about dusk. "My son was frightened. He used to come out in the evening with me to empty the garbage but now I can't pry him out of the house."

Health officials said they hope the birds, some of which are migrating south but apparently are confused by the unseasonably warm weather, find another roost soon, even if it's a neighboring county.

"The biggest problem is the noise and the droppings on cars and clothes hanging out to dry," said Robert Pritchett, Alexandria's director of Environmental Health. " . . . After the shooting they will probably go away, but they may just move to another part of the city. Hopefully they'll go to Fairfax."

"They are not welcome here," said Martha V. Pennino, vice chairman of the Fairfax Board of Supervisors. "And frankly, I resent that statement. Even if meant in jest, these birds are a big problem, and we certainly don't want them."

Pritchett said, however, that along with the annoyance, the birds pose a health hazard. He said the droppings, which in some areas near the Holmes Run Parkway have created a white coating on cars and sidewalks, feed a dangerous soil fungus that, if inhaled, can cause histoplasmosis, a respiratory ailment similar to tuberculosis.

Philip Eggborn, bird control supervisor with the Department of Agriculture and Commerce in Richmond, said Alexandrians aren't the only ones stepping outside with extra caution this week. "There are 50 to a 100 [of these] roosts in the state right now," he said, and "we're recommending some kind of loud noise" to harass the blackbirds and starlings out of their homes.

In selecting the "bird bombs," which will cost about $500, health officials said they discarded many other devices such as 6-foot rubber snakes that were used in the White House garden last winter to scare away starlings, a U.S. Fish and Wildlife Service distress call tape and artificial "scare tactic" owls.

To inform residents that two policemen and four health officers will be shooting explosive projectiles from the pistols and shotguns next week, City Council member Redella (Del) Pepper suggested at the Tuesday meeting that the city be "papered," meaning that leaflets be distributed.

But other council members, including Mayor James P. Moran, apparently misunderstood her and, amid laughter, asked Pepper if she really thought putting toilet paper all over the city was the answer to catching the droppings.

"I consider this a very serious matter," she said yesterday. "I am not sure why they were giggling."