It's always seemed appropriate somehow that Frank Zappa "discovered" Adrian Belew. Even before being recruited into Zappa's orchestral rock ensemble of the mid-'70s, guitarist Belew was exhibiting his mentor's sensibilities on technique and musicianship and his keen sense of the absurd.

But as Zappa has grown increasingly eccentric and unpredictable, Belew (who performs at the Wax Museum tonight) has managed to rein in his avant-garde rock tendencies through his strong sense of the language.

On his second solo album, "Twang Bar King" (Island 7 90108-1), Belew demonstrates his writing instincts as often as he does his formidable, stylized technique. Many of the images running through last year's "Lone Rhino"--a fascination with animals, the imperfection of love, American landscapes as viewed from a passing train--recur here, and Belew is getting more adept at evoking them through sound and words. Belew's wonderful rhinoceros makes yet another appearance in "Sexy Rhino," as does his vaguely zoological creation, the momur, in "Fish Head." These occurrences seem part of a honing process, as if Belew is determined to make the images as vivid in the listener's imagination as in his own. He proves quite adept at this on "The Rail Song," coaxing such a convincing old streamliner out of his guitar that it seems to roar into your living room.

Except for these occasional dead-on effects and the two instrumentals on the B side, however, Belew doesn't use his new songs as a showcase for his renowned technical prowess. He eschews flexing his musical muscles in favor of using them to gently lift the songs to eye level. His ability to blend his guitar sounds into the accompanying instruments, particularly Bill Janssen's sax, is so sharp that it's sometimes difficult to separate the two. Even on the title track, a half-mocking, half-boasting boogie, Belew's guitar sounds more like a brightly honking sax than the screaming Stratocaster implied in the lyrics; the tune has all the weird atmospheric trappings of the bar scene from "Star Wars."

Belew shuffles moods and modalities with astounding sleight of hand. "I'm Down," the one non-Belew composition, pays homage to his Lennon-McCartney roots, as does "She Is Not Dead," an eerie dirge whose bagpipe-guitar effects (taught to Belew by Zappa himself) lends it a "Strawberry Fields" texture. "Fish Head," a ballad about a blissfully innocent grotesque, treats its subject with giggly compassion, while the ethereal "Ballet for a Blue Whale" is as enchanting as any of Belew's instrumentals for King Crimson.

The most charming song on the album is "The Ideal Woman." Belew has taken his tape recorder to the street, to ask pedestrians to describe such a woman. It's a technique employed on the King Crimson song "Thela Hun Ginjeet" and the results are a funny, fey commentary on how various are the eyes of the beholder. "Tall, pretty, thin, blond," murmurs one timid woman; "Pretty with hairy legs!" asserts a confident male. So fine-tuned is Belew's ear for the natural rhythms of spoken English that one half imagines him adding to his request, "and could you give me that reply in a funky 7/8, please?"

In the end, it's Belew's humor that makes one forgive his occasional ear- bending, vaguely East Asian progressions and his wide-eyed, unabashed sentimentality. "Twang Bar King" offers plenty of commonplace, humanistic observations to warm up its avant-garde coolness, which is, of course, what makes Belew more than just a great rock guitarist.

Zappa's humor, on the other hand, has always tended to bite too hard. One of rock's most prolific artisans, over two decades he has managed to assail everyone and everything several times over, often couching his lyric attacks in ingenious musical ideas. The novelty of his dispeptic inventions wore off long ago, causing his audience to dwindle and his music to go largely unappreciated.

"Zappa, Volume I" (Barking Pumpkin 023) is a well-advised retreat from the bad habits that have plagued his career of late. Performed by the London Symphony Orchestra and directed by Zappa, it is a random overview of Zappa's work. If that sounds funny, it is, sort of. But whimsically so, because the music is tempered, both because it's treated and performed seriously and because, removed from their highly thematic, often mean-spirited contexts, the songs are more accessible.

This is not schlocky, pseudo-progressive rock along the lines of "Procol Harum with the London Philharmonic" or Emerson, Lake and Palmer's embarrassing forays into the classical genre. The arrangements are tasteful and well-executed, as only perfectionist Zappa would have them, revealing him as the risk-taking contemporary composer he is.

The standout track here is "Mo 'n' Herb's Vacation," though some will complain about its length. It's a three-movement study of the endless possibilities of style and structure, as well as a delightfully entertaining pop song, of the sort we used to regularly expect from this quirky avant-garde artist. "Zappa, Volume I" is the most pleasant surprise he's offered us since daughter Moon Unit.