If you come across what appears to be a sick bird while raking leaves this fall, look twice before picking it up. It may be a bat with rabies.

And bats bite.

Reports of bat bites already have reached a near record level in Maryland this year, and millions of the winged mammals are expected to sweep through the Washington area in coming weeks during their annual fall migration south, local health officials say.

Although the percentage of rabid bats in a flock is relatively low, up to one-third of those that fall to the ground may carry the deadly rabies virus, said Dr. Kenneth L. Crawford, Maryland's public health veterinarian.

Maryland's present bat population of 4 million is expected to swell as high as 12 million during the next two months, as the creatures move south from the cold in New England and Canada in search of insects to feed on, Crawford said.

Although most bats are only passing through on their way to southern states and the Caribbean, many area homeowners may find themselves unwillingly hosting bats this year because of minor storm damage to their homes.

Migrating bats search for basements, attics and garages where they sleep during the day, Crawford said. This year's summer storms, particularly Tropical Storm David, have created cracks under roofs and holes in screens. A hole as small as three-eights of an inch across can convert an attic into a bat motel, he said.

Of the 68 people bitten in Maryland this year, 32 have undergone the painful series of rabies shots that cost about $1,000 per person, a state health department spokesman said. Many were residents of Prince George's County, where 28 of the reported bites occurred.

Because of county reporting policy, that figure represents "contact' with bats and "scratches or licks" as well as definite bites, said Arthur Thacher, director of the country's bureau of epidemiology. He said in some cases, children were found handling bats, and it was uncertain whether the bat had bitten any one.

Bats are particularly dangerous because they can carry the rabies virus for up to three years before dying of the disease. A bite or even contact with the saliva of an infected animal can cause rabies in humans or other animals. The symptoms usually appear in about five weeks, and the disease virtually always is fatal.

People who are bitten should begin treatment within 24 hours if they are unable to bring the animal to authorities for examination of its brain to determine whether it is carrying the virus, said Dr. William Winkler, rabies specialist at the Center for Disease Control. The bite victim receives an initial injection of antirabies serum, then 21 daily vaccine injuections followed by two booster shots.

The injections, which are given in the fat of the stomach, cause skin irritation in most patients, a flu-like illness in some, and dangerous reactions in a few. A new, safer vaccine has been tested but still is awaiting final approval by the Food and Drug Administration, Winkler said.

He said a study of apparently health bats captured along flight paths in the southwest United States found that only one half of one percent carried rabies. Fifteen percent of bats found on the ground had the disease. In Maryland, Crawford said, one-third of grounded bats are rabid. He theorized that the virus, which affects the nervous system, weakens the bats and they come to earth to rest.

Crawford advised home owners to check windows, attics, porches and basements for small holes through which a bat might enter. If a bat does get into a living area, it usually will find its way out if left in the room with the lights off and the doors and windows open to create a crossdraft, he said. Leaving the lights on will cause the animal to seek cover in draperies and dark corners.

If the bat refuses to leave on its own, it should be "flocked out of the air" with a broom or tennis racquet, objects porous enough to fool the bat's built in sonar, Crawford said. Bats easily avoid a solid weapon. Once captured in a plastic container, the bat can be disposed of or, if it has bitten someone, killed for examination, Crawford said. But it should not be touched.

He suggested that area residents make certain their pets' rabies shots are up to date. If an unimmunized pet is bitten by a bat that cannot be examined for rabies, the animal must either be killed or kept in strict quarantine for six months.