A hundred or so hopeful throats hum through a vocal scale exercise at Howard University. "That was beautiful," says the teacher. Nice to be congratulated by a teacher; better yet Deniece Williams, the cherubic R&B singer, who parades around under an explosion of blond tresses and sings for big money.

Yesterday at Howard's Fine Arts Auditorium, Williams led a workshop in commercial vocal performance, part of an ongoing Howard instructional series on all aspects of the music business, from jingle writing to music videos. And the students listened attentively to words from a pro, as Williams spoke of how to make demonstration cassettes ("Don't get no cassettes for 99 cents, now. They're only good for two plays and then the tape goes woooaaaaaaaw") and how to keep a voice working for several performances ("it's all about longevity . . . [drugs and smoking] affect the voice -- you can't sing the way you want and be healthy").

When a professional is up there on stage talking about success, it can raise dreamy hopes, Williams acknowledged before the workshop: "As we all know, everyone is not going to be a successful entity in the music industry, but I'm telling them there are other ways to still be in the industry, as teachers and studio professionals . . .

"I'm very committed to this," she said. "I want to make sure that when the students get there, they know what happens."

Indeed, for Williams, the visit wasn't so much a straight lecture as it was a good-will mission for hopefuls: encouraging students, signing autographs, meeting with the school dean and posing for anyone clutching an Instamatic, not to mention trying to ignore the CBS film crew dogging her from auditorium to elevator and back again.

Stopping Williams in a hallway, a young man with a timid voice, whose ambition battled politeness, was asking her if she . . . well, if she wouldn't mind him interrupting . . . he has a high range and wanted to know if it would be salable.

Oh sure, said Williams, citing singer Eddie Kendricks. She promised further truths later.

"I was 17 and working in a record shop after school," she said, remembering her professional origins in Gary, Ind. "My teacher brought some talent scouts to look at me. They listened and then they promised me fame, fortune and contract, and all I got was a contract."

After a brief stint as a nursing student at Purdue University, she decided to try again. A friend who knew Stevie Wonder arranged an audition for her and she was accepted as a backup singer for Wonder. She joined him in 1971, participating on every Wonder album between 1972 and 1976, as well as contributing to albums by Roberta Flack, Minnie Riperton and others. "But I decided I wanted to be a songwriter."

And now, Williams, 35, is there, singing both R&B and gospel albums, notching hits with a range that extends three octaves. She has been produced by Maurice White of Earth, Wind & Fire, Ray Parker (of Raydio) and Philadelphia Sound maestro Thom Bell. And now she is at work on two albums, one a pop release ("Hot on the Trail," to be released in April) and the other a gospel offering ("So Glad I Know," slated for June).

Says Williams about reconciling her commercial and gospel personas: "It's not a question of being a religious artist and a secular artist. I just happen to be a Christian who happens to be an artist. I try to be careful about what I sing. Because you become a role model for kids. If a song is not valid or something that says something useful, I'm not going to do it. With the Christian music, there's more of an out-front message . . .

"But it's not as though I'm schizophrenic."

And then it was back to the good-will mission, introducing guest lecturer, singer and tap dancer Hinton Battle to the class, and talking to more ambitious would-bes and well-wishers in the hallway.

"I think the more people you approach the better," she said to one student. "Just persevere."

"You have to pay the dues," she said to another.

"Oh yeah!" said the student.