The San Francisco Chronicle JUNE 5, 1990, TUESDAY, FINAL EDITION Sinead O'Connor's Serious About Her Rock Joel Selvin, Chronicle Staff Critic An obscure gem of a song written by Prince, an agonized, soulful vocal performance and a solitary tear shed during the making of the video and suddenly Sinead O'Connor is the hottest talent on the music scene. Both her wrenching version of Prince's ''Nothing Compares 2 U'' and her album, ''I Do Not Want What I Haven't Got,'' scorched up to the top of the charts within weeks of release. Her face graced the cover of Rolling Stone and she splashed into the headlines by pulling out of a scheduled appearance on ''Saturday Night Live'' in protest over the humor of guest host Andrew Dice Clay. Her shaved head, allegedly shorn following a suggestion by a record company executive that she do something more ''girly,'' made her one of the most memorable faces of the '90s. She has been anointed as the first new star of the decade. AN EXCITED FOLLOWING Appearing in two sold-out shows Sunday and last night at the Berkeley Community Theater, O'Connor attracted the kind of excited, almost hysterical following that marked her concert as a genuine event on the music scene. She will follow the relatively intimate performances with a return engagement at the more massive Greek Theatre in September, but the shows this week will serve as her Bay Area coming out. At age 23, the impassioned Irish pop iconoclast looks like a good bet to become one of the most persuasive talents of her generation. Her highly personal compositions read more like diary entries than pop songs. These heartfelt confessionals cover the gamut of emotional colors, from desolate loneliness to fiery rage, and she matches the moods with dramatic shifts in her powerful voice, from a whisper to a scream. CRIES OF ANGUISH Opening in a hazy crossfire of spotlights, the music oozed behind her, as she gingerly made her way through ''Feel So Different,'' working up to the climactic anguished cries. She used her unusually loud voice like a child with a new toy, gunning down lyrics that could have been more effectively understated and understating others that consequently got lost in the murmur. She made a point of pronouncing certain vocal nuances -- from the clicks of her tongue against the roof of her mouth to her sharp inhalations between lines -- as if to share the honest labor of her artistic effort. THUMBING HER NOSE A lot of her style goes intentionally against the grain. Her rigid anti-show business stance showed from her refusal to face applause, but walking directly offstage as soon as she was done singing a song, to her concentration camp haircut and the untucked T-shirt. Who is she kidding? An anti-fashion statement is still a statement and a little bit of pretension goes a long way. But she clearly doesn't want to chance anybody missing that she is an Artist with a capital A. She opens her style up remarkably, able to fit a cappella Irish folk music next to boombox dance-rock. She even wheeled a tape recorder out onstage to accompany one song. Her sound ranged from folkish ensemble pieces with her playing 12-string guitar to full electric rock in high wail. She used various configurations of a five-piece band that included the inestimable services of keyboardist-guitarist-vocalist Suzie Davis, formerly of the Bay Area. It was a tour de force performance of a style so highly personal that the components could have only been assembled by one individual imagination. No committee at some record label could have contrived this model. She is dealing with some highly potent, powerful forces. And when the elements come together, she is as bright as a flash of lightning, as forbidding as a clap of thunder and as refreshing as a rainstorm. If she ever pulls them together for a sustained length of time, watch out.