If your knowledge of singer-songwriter Dennis DeYoung is limited to the soaring signature melodies and vocals he provided for his rock band Styx, you may be surprised at the songlist for his latest disc.

Someone to Watch Over Me. On the Street Where You Live. Summertime. Once Upon a Dream.

Oh, no! Not another show biz wash-out trying to relegitimize his career on Broadway, the industry's chief repository for TV's unemployed action heroes and moonlighting soap starlets.

No, not at all. Not Dennis DeYoung, who has a genuine knack for musical theater and has sidelined the band out of choice, not circumstance.

DeYoung, 47, proved his dramatic mettle for two decades fronting the theatrically rooted Styx, then again last year on tour in Jesus Christ Superstar, and now with the just-released disc, 10 on Broadway.

The album, which features no electronic instruments, also includes music from Les Miserables, Chess, Cats, and the West End production Time, among others.

Though the transition from rock to rock opera and show tunes would seem a snap, particularly for a singer so suited to the style, DeYoung says he has had his share of frightening moments.

"Have you ever seen a deer on the highway late at night?," DeYoung said of his first tenuous weeks on tour as Pontius Pilate in Superstar. "I took the thing because it was not a major role. I figured I could play a bunch of cities, but not necessarily go to Broadway on my first attempt. This way, if I stank, I could get the hell out before anybody noticed.

"But I must say in as fair and as humble a way possible that I actually got pretty good at it by the third or fourth week," he said earlier this month during an interview with the Sun-Sentinel. "Though every show was always a nerve-racking experience. ''

When Atlantic Records chief Danny Goldberg caught him in Superstar, he offered DeYoung a contract on the spot - but not the usual kind of contract. This new deal called for an album of show music, not unlike discs from crooners such as Mandy Patinkin and Michael Crawford.

Though promoters had offers out for a lengthy Styx roadshow, DeYoung passed to sing Broadway instead.

"I feel like the luckiest guy on the face of the Earth. I've had an incredible opportunity handed to me.

"I can go back and do the Styx nostalgia thing anytime. We can do in 10 years what we could do this summer or five summers from now. And the Panozzo brothers [twins John and Chuck, who played drums and bass in the band, respectively) are retired. I think they're in the olive oil business."

So after 20 years with Styx, and then six months on the road with Superstar, DeYoung was ready for greater challenges.

"That's enough crucifying for one life - 39 lashes a night and 78 on the weekend," he said.

Plus, he's not one for trends. Much of what's new in rock doesn't impress him. He won't alter the classic Styx sound to sell records in an industry he's not sure he believes in anymore.

"Flannel makes me itch," he says of the Seattle sound. "So much angst, so little time. They think life stinks. You wear a bone in your nose. It's all window dressing. But what's this music about? You just can't keep giving people negative images. It's garbage."

So what's next for him - a star turn in Guys and Dolls? Carousel? For the man who wrote rock staples such as Come Sail Away, Babe, The Grand Illusion and The Best of Times, the fantasy now is the old Robert Morse role in How to Succeed in Business Without Really Trying.

"Now that's a great show."DeYoung is also writing a musical based on a historical novel.

Married for 25 years, he and his wife Suzanne have two children, ages 23 and 14.

"She raised them on the road. We always stayed together as a family," the singer said proudly.

Throughout his career, they also kept a home base on the south side of Chicago near other family members.

"I am what I am. Whatever it was that made me what I am, I thought I should stay around and be that.

"My views are simple," he says of his recipe for happiness. "If you're gonna make a commitment, particularly marriage, stick to it. If you can't compromise, you've got no chance.

"Americans are really good at throwing their hands up and walking away from things. If you think marriage is gonna be easy, don't do it because when there are children involved, you screw up the rest of society."