WITH THE DEATH of Dinah Washington 20 years ago, an entire school W of jazz and blues singing nearly vanished. The Baltimore-based Ethel Ennis is one of the few remaining authentic interpreters of double entendre lyrics and the more direct "evil gal" blues. She opens at the Maryland Inn in Annapolis, for two weeks Wednesday.

Ennis, whose history includes European tours with Benny Goodman, Newport Jazz Festival appearances and an a cappella delivery of the national anthem to the 1973 presidential inauguration, has a rapport with her audiences akin to the give and take of a storefront church service. "It's like coming into someone's home and you try to break down the barriers right away," she explains. She dubs her risque' persona "the other Ethel," and defends her unexpurgated version of the Bessie Smith classic, "Empty Bed Blues": "It's not as explicit as some of the things you hear today and it's all tongue-in-cheek anyway." Do club patrons ever take her the wrong way? "No, they love it," she laughs. "I guess it's a release."

But that's only one side of Ennis, for she can also bring ballads across with warmth and sincerity, and on up-tempo numbers she can scat to beat the band. "From now on in until the day I die," she said, "my dedication is to feed the spirit."