Bats flew peridically through her duplex apartment, bat exrement appeared in her kitchen and dining room, and as she lay in bed at night, Janet Mason says she could hear "a menagerie of bats inside the walls and inside the ceiling, scratching, fluttering and occasionally crying."

It was like that for the entire year she lived in the Daleview West Apartments in Riverdale, Mason says, and so she has filed suit in Prince George's County Court against the former owners and managers of the apartment complex. She is seeking $14.5 million in damages for mental anguish and physical illness she claims she suffered as a result of the bat infestation.

Athletic and happily employed as a bartender until the summer of 1978, Mason says her life began to disintegrate soon after the bats appeared in the apartment where she and her two sons lived.

Mason, who had no previous history of mental problems, suffered what her psychiatrist termed "vicious nightmares" about being attacked by bats. During one of the nightmares, she severely scratched herself on her legs and body.

A psychiatrist diagnosed Mason's condition as depression and anxiety due to her bat phobia and hospitalized her for a time. The doctor said that Mason's various physical ailments, including stomach problems, resulted directly from the bat episode. Mason's emotional difficulties were compounded by an inability to convince anyone of the seriousness of the bat problem while it was occurring.

Mason also said her sons had touched a dying rabid bat in the apartment complex playground in the spring of 1979. As a result, each had to undergo a series of 25 rabies shots.

Repeated complaints to the former managers of the apartments, Zalco Realty of Silver Spring, were fruitless, Mason said. After one particularly harrowing night in November 1978, in which Mason, then recovering from surgery, was terrorized by several bats in her home, the management did send repairmen to close the wall cracks through which the bats had entered. However, Mason charged that the repairmen used old boards and rusty nails to do the job and failed to shut out the bats.

The bat epidemic had reached such severe proportions at Daleview West by July 1979 that the county was about to declare the dwelling "unfit for human habitation." A Baltimore exterminator was then called in, and he successfully killed the bats.

But by that time Mason, who had lived in the apartments since the previous August, had moved.

Mason's suit also names Daleview Associates Inc., the former owners of the apartments, and two exterminating companies, Chase Exterminating of Silver Spring and Easy Maintenance of Beltsville, which allegedly failed to eliminate the bats.

None of the defendants in the suit could be reached for comment yesterday.

Mason said yesterday she is seeing a therapist three times a week, and is not capable of holding a job.

"I just can't keep my mind on one thing all day. This is something I have to live with, but it brings back so many painful things. I'd rather have a python right next to me than a bat sitting in front of me. I think this is something that will be with me forever."