What if you were a disc jockey with a lovely voice and everyone thought you were a sexy, beautiful woman but you knew you weren't?

You might meet the question head-on, as Donna Halper does. She's a midday DJ for WAVA-FM who doesn't spare herself an insult: "I really do think I'm ugly, have been most of my life - nice body, but that's about it," says Halper, whose honeyed voice earns her mash notes.

Ever since she was a little girl in Boston in the Fifties, Halper realized she was different from her playmates because she wanted a career. Now 31, she's worked as a teacher (she has a master's degree in English and one in counseling), social worker, writer, prison guard, publicist and DJ in several cities.

"I'm just a humble Jewish from Boston trying to make a living," says Halper, who knows the inadequacy of that description. She is a feisty feminist whose interest in prison reform and delinguent children was cultivated when she lived in Cleveland and New York. Since her arrival in Washington last November, when the WAVA-FM changed from an all-news format to "adult rock," Halper had worked as a Big Sister. Unmarried, she admits she wouldn't mind changing that status soon.

"Listen," she says in a sexy murmur, "you want me to wrap up my voice and send it to you?"