TIRED of the unvarnished truth? Beauty is youth, too; and a little melodic mysticism can be mighty restful, especially in pop music. Armed with a stunning voice, a Kate Bush sensibility and a parochial school poeticism, Karen Peris and The Innocence Mission wander lullingly through a child's garden of virtues.

This is a band that deals in ideals, and why not? The first moral imperative is aspiration. After that comes adolescence and after that, perhaps, art. Peris, a post-Romantic visionary ("the 19th century evokes innocence to me"), proselytizes so winningly that it's easy to forgive the faint trace of self-absorbed confessionalism in her earlier lyrics.

" 'Innocence' stands for all the good things of childhood, the things we should try to hold on to," says Peris. "It's a state of mind. And 'Mission' is a kind of place to us, not a {crusade} . . . I see it as an old house filled with all these childhood memories."

This is a young band in both senses of the word (Karen Peris, at 25, is the oldest of the four). The weakness of mysticism is that it often mistakes metaphor for meaning, when it really only provides a mirror. It needs a darkness, a shadow-life, to give it depth, a dichotomy that has only begun to grow on Peris.

Yet naivete' is not necessarily a failing here. Peris writes of what she knows -- her family, her husband (Mission guitarist Don Peris), her own imaginings -- and there are no passages so poignant as those of adolescence. As she says, about half of her lyrics are based on personal experience, and the other half on characters from books and dreams; of those, most are characters "on the outside looking in."

Consider "I Remember Me," a lament placed in the mind of Anastasia Romanov (or rather, Anna Anderson, the woman who persuaded many people that she was the sole surviving tsarina). Defiantly plaintive and personal ("I know who I am; I think I should know who I am"), it gains far more from its underlying archetypal impact; the amnesiac, unacknowledged Anastasia is also the most famous embodiment of every child's conviction that he or she is a changeling, a princess among peasants.

Peris has a voice like a Toledo blade: silver on steel, both shining and slicing and with a shivery quality in the higher registers that recalls the similarly visionary, pre-formula Dolly Parton. The group is maturing rapidly, and their stage poise is impressive (from Amish country, Lancaster, Pennsylvania, they've been together since high school). They have been signed since December to A&M Records, but label execs are still huddling over a producer.

In the meantime, they're working it out on the road. The Innocence Mission headlines Saturday at the 9:30 club.

IT'S A LONG WAY from innocent, but there is a particular fundamentalism about rockabilly that attracts another sort of purist.

It's that aura of reckless abandon -- the rollicking, apostate gospel piano, the gutteral Bronx cheer of the sax, and above all the unsissified rawness generated by those chesty solid-body guitars that reverb a quarter-tone wide. Even as propounded by its relatively "decadent" sophisticates, like the street-smart Marshall Crenshaw or the loon-cry Chris Isaak, modern rockabilly has an adolescent swagger that puts the hormones in high gear.

Local boy Bobby Smith is not only a first-class practitioner of the time-honored art of V-8 guitar, he's an inspired rockabilly writer whose Ripsaw Records EP, "Two Sides" (Ripsaw 221), swings like a juke-jump gigolo.

Smith's writing, which on the surface adheres to the rockabilly straight and narrow (musing on love, cruising on the corner), packs sly surprises. On "Tough Girls," a ballad for the downtown Lolitas, Smith croons, "I see you standing with your feet half-pigeoned / 'Cause high heels make you stand so tall."

His singing style also bows to the fundamentals: There's a single and perfectly persuasive hiccup, sotto Holly, in the refrain of "What Do I Hafta Do?" and a come-on echo of the young Rick Nelson in "I Wanna Be With You." The cover of Crazy Cavan's "Both Wheels Left the Ground" on the records gains even more chug from Danny Gatton's locomotive solo, but this is a band best seen and swung to live.

Smith, who has spent the last 10 years slugging it out on the Maryland bar scene, performs Friday at the Kazz Club above the Onyx; next Friday and Saturday at Captain White's in Silver Spring and June 10 at the Roxy.

BLUES COMMENCEMENT: The Blues Alley Youth Orchestra, a master-class ensemble made up of high school all-stars, winds up its '88 spring season with a one-night home stand Wednesday at Blues Alley. Three of the members, Scott Denett of South Lakes (guitar), John Jaksch of Chantilly (electric bass) and Michael Nilsson of Winston Churchill (tenor sax) have just returned from the Downbeat Jazz competition in Orlando, where the Denett/Jaksch band took a third place; the Montgomery Country Jazz Honors band, with Nilsson in first chair, took a silver medal, and Nilsson himself was named a Downbeat All-Star.

The youth orchestra, which gave its debut performance in December, 1986, operates under the auspices of the non-profit Blues Alley Music Society. Dizzy Gillespie serves as the group's chairman, and traditionally the program opens with a Gillespie composition -- this time, probably "Night in Tunisia." Bob Israel is the group's conductor, and Leigh Pilzer his associate. Admission $10. 337-2338.