With its perfunctory poofs of smoke and squint-inducing light splashes, Petra looks like your typical corporate rock band.

But take another glance. Peel your eyes off the stagey costumes, ignore the pounding percussion and listen -- yes, listen -- to the lyrics:

I'm clean clean clean before my Lord

Like a spotless lamb I'm blameless in His sight

With no trace of wrong left to right

I'm clean clean clean.

That's right, heavy gospel.

"After we're done making music and not on the road anymore, the message is what's going to live on," says lead guitarist and songwriter Bob Hartman by phone from his home in Hendersonville, Tenn. A former Bible teacher, the 35-year-old musician uses the intensity of rock and the lessons of Scripture to influence the young.

Petra (Greek for "rock") has sold more than a million albums, toured the continent extensively and established a well-oiled organization that fights world hunger, coordinates youth counseling and produces a quarterly newsletter containing an unusual mix of news from the band and The Book.

The group has won several gospel awards and increased record sales and attendance numbers each year. Although the Christian rock circuit is not exactly glutted with talent, overcoming antirock bias in religious circles proved a formidable task.

"When we first started out, people said we were demons possessed," says Hartman, adding that some have denied the band members -- all of them born-agains -- their Christianity, a particularly painful slur.

Since the band's incarnation in 1972, many critics have seen the light. Now it faces another hurdle: the secular world. Petra has signed with a major record distributor, filmed its first music video and set its sights on the mainstream rock terrain currently dominated by groups such as Journey and Foreigner.

Will Petra (which performs Friday at Merriweather Post Pavilion) be able to cross over? Can an evangelical group share the airwaves with Prince's libido and Madonna's sighs?

So far, no.

MTV rejected the video, in which a blindfolded man rips off the cloth, sees the blue skies and persuades others to follow him. And most commercial stations did not pick up the single "Beat the System" (from the album of the same title).

Hartman says the radio industry has "some kind of prejudice" about Petra's music, noting that several stations did not play the single despite its popularity among listeners. In Dallas, one station dropped it even though it won a battle of new songs, Hartman says.

"I'm not on a persecution complex," he adds. The album has landed in secular record stores, indexed among other rock albums, and the video has been screened on "Night Tracks" and HBO. "We just wanted the music available and accessible to a wider audience, and that has happened."

Even if Petra doesn't hit the Top 10, it can already claim a devout following. Among the most requested numbers are "God Gave Rock and Roll to You" and "For Annie," a song about teen-age suicide. "We still get letters from kids saying, 'That song stopped me from committing suicide,' " Hartman says.

In concert, Petra has the kick of a revival. In the middle of the show one of the band members introduces a song about the Christian view of death by talking about his recently departed mother. The performance of "Hollow Eyes," about world starvation, is accompanied by a compelling video and a request to sponsor a child's clothing, feeding and Christian education. And afterward the group tells the audience that there are pastors in the arena who will talk about Christianity with anyone interested. More than 100 youths participate at each concert, Hartman says.

Petra works hard at communicating its message within the sleekest "techno-rock" format -- amplified at about 110 decibels, with 23 different drum beats, synthesizers and glossy vocals from Greg X. Volz, whose four-octave range and choir-honed voice attracted REO Speedwagon's attention. Volz snubbed the group's offer to sing lead, however, finding little value in the band's direction.

Hartman knows Petra's albums will become dated and he won't be able to prance around onstage forever, and he laughs when posed with the idea of future Christian rock bands doing cover versions of his songs. But he becomes serious when talking about life after Petra.

"We can't go on the road forever," he says, "but I'm still going to have that message living in my heart."