Manhattan is like a moist towelette this evening, but Cybill Shepherd is having an excellent hair set, despite the humidity. The 44-year-old actress, once again trying to jump-start her idling singing career, is stretching her vocal cords at New York's exclusive Rainbow Room for a three-weekend engagement. And she is worth it at least in the eyes of this capacity crowd of Moonlighting fans.
The teenage cover girl-turned-TV star-turned-Preference by L'Oreal spokesperson's very white, suspendered pants and sleeveless undershirt compete with the moon outside for brightness. Her shiny, manageable locks bounce confidently. Critics may slam her singing (in a review of her Cybill Does It...to Cole Porter album, The Detroit Free Press asked, ''What did Cole Porter ever do to her?''), but she does not care. Backed by a small jazz combo (she dates the keyboard player), Shepherd defiantly belts out country songs (''Talk Memphis''), jazz standards ('''S Wonderful''), even opera (Verdi's ''Quando Men Va'') with gushing diva abandon. Like a true chanteuse, she occasionally languishes on the baby grand. What she lacks in Mariah Carey-like range, she makes up for in theatrics pumping the perfect amount into each number and every bit of between-song patter. ''I did the nasty with Elvis,'' she says pertly, ''and there was one thing he wouldn't eat before he met me.'' The audience titters nervously as she pauses dramatically, her Breck girl tresses cascading about her head (and shoulders). ''Papaya,'' she says finally, her sex-imbued Memphis lilt lowering an octave. No offense taken; one fluff of her perfect 'do and all missed notes and tacky repartee are forgiven. The audience leaves smitten, with perhaps a touch of hair envy.