Both Stevie Nicks (who performs at the Capital Centre tonight) and Rickie Lee Jones approach their music with a fervency uncommon in mainstream pop. Nicks' songs evoke a mystical, deeply romantic world that is inviting but ultimately inaccessible to the listener, while Jones opens up her interpretations in such an intensely intimate manner that the audience feels immediately privy to the experiences she describes.

Nicks, like Jones, shares a frankness and vulnerability made popular by Barbra Streisand, Laura Nyro and Joni Mitchell, but she lacks the vocal skills and songwriting ability to elevate her expressiveness above sheer pop drama. Her second solo album, "The Wild Heart" (Modern 90084-1), is animated but far from eloquent.

Part of the problem is her persistence in playing the quasi-mythological Welsh witch that defined and limited her participation with Fleetwood Mac. In a typical Nicks song, images from the occult are slung together willy-nilly with romantic fantasies to create billowy but incomprehensible themes. Hers is a style that lends itself better to a visual context than to vinyl, and her studio albums seem only to draw attention to her narrow vocals and formulaic compositions.

The most embarrassing example of Nicks' actressy pretensions occurs in "Nightbird," in which she laments the state of her eye makeup and summer footwear while lamely attempting to cast herself as a metaphor for mysterious love. "Beauty and the Beast" is a better attempt, anchored on a real story; a softly swaying waltz, it's also the album's best cut musically.

Elsewhere she rambles, especially on the title track, which contains some four-plus minutes of chorus repetition. Dedicated to a friend who died, it's a pretty, rocking song with some catchy phrases and good melodic hooks, but Nicks gets carried away in her expansiveness of emotion and overstates the tune.

On "Wild Heart," Nicks' voice is in its best form since early Fleetwood Mac--less thin and raspy, more rocking and self-assured. Determined to remain a solo artist, she is nonetheless at her most beguiling in the company of other vocalists, as past collaborations with Kenny Loggins, Tom Petty and others have shown. Her duet with Petty on her debut album, "Bella Donna," proved a durable, engaging rock hit.

Perhaps in an effort to repeat that success, the two perform another Petty-penned piece here, "I Will Run to You." Unfortunately, Petty sounds cranky and unmotivated on this one, as if it represented more an obligation than an opportunity. The guitar phrases are stale leftovers from his "Damn the Torpedoes" album, and the lyrics rival Nicks' own for inane sentimentality.

Nicks continues to be one of the most passionate female vocalists in rock music. What she has yet to acquire is the ability to strike a more universal balance between fantasy and reality, to invite her audience to some common ground where they might share the source of that passion.

Rickie Lee Jones' most recent release, a seven-song EP titled "Girl at Her Volcano" (Warner Bros. 1-23805), demonstrates her considerable skill at exacting emotional involvement from her audience. In addition, this album, which contains only one self-penned composition, shows Jones getting as much emotional mileage from other artists' material as she has previously gotten from her own. Her range and technical ability are as awe-inspiring as ever, but here they become formidable tools that she uses to manipulate texture and tone from one moment to the next.

On the two live tracks, "Lush Life" and "My Funny Valentine," the audience responds by hanging onto every nuance, cheering or even shouting replies at a phrase here, breathlessly silent within a pause there. Particularly on "Lush Life," Jones uses their enthusiasm to draw them even deeper into her interpretation, thus weaving her audience into the context of the song.

Jones has a knack for making the most familiar standard emphatically her own. Leaping from a tristful whisper to a chill-raising shout, she breathes a jazzy new anguish into the 1966 Left Banke hit, "Walk Away Renee." And on "Under the Boardwalk," she weaves through the male voices of the chorus with such spontaneity and verve that the old Drifters favorite is transformed into a tapestry of youthful joy.

Of course, Jones' highly stylized approach has its perils, chief among them the risk of overindulgence. On "Rainbow Sleeves," a Tom Waits tune released earlier this year on the "King of Comedy" soundtrack, she slips from heartfelt nostalgia into a weepy childlike pose that does justice neither to her womanly soprano nor to the intent of the lyrics, which concern renewed strength through companionship. Yet even "Rainbow Sleeves" has its thrilling moments, as does her own "Hey, Bub," a ballad sketch that captures the whimsy and tenderness of a remembered friendship.

Jones has taken great pains to assert that "Girl at Her Volcano" is not the "next" Rickie Lee Jones album, but merely a sampling of favorites she has enjoyed performing in her scattering of club dates over the past few years. Still, it will do just fine to hold over those who've come to regard her as the most impressive pop vocalist since the young Streisand.