One was the most popular female singer to emerge from the Motown factory, the other the most important singer to emerge from the disco assembly line. For Diana Ross, of course, it started in the '60s with the Supremes and Berry Gordy's firm guidance. For Donna Summer, it began in the mid-'70s when Giorgio Moroder's high-tech Europop productions cast her as a sex goddess for our times.

Over the years, Ross has sustained her superstar status without abandoning the protection of other people's influence; with the exception of an occasional smash single like "Muscles" or "Endless Love," she seems content to put out safe albums that please, but seldom thrill, and do absolutely nothing to clue us in to her personality.

Summer, on the other hand, is emerging as one of the more interesting singers of the times, constantly pushing herself, taking chances, unveiling her most private emotions. Until recently, her post-disco work was uneven, but her latest album, "She Works Hard for the Money" (Mercury 812 265-1 M-1), is a revelation. Several years ago, Summer declared herself a born-again Christian, but except for the joyful affirmation of "I Believe in Jesus" from the "Wanderer" (her last full-scale rock-oriented effort), there has been little in her work to reflect that profound change.

There's a reason why it's taken Summer this long to shed the "disco queen" skin that's clung to her since "Love to Love You Baby." Previous producers--Moroder and, last year, Quincy Jones--simply took advantage of Summer's looks and dynamic voice--casting her as everything from the streetwalker of "Bad Girls" to the naif of "No More Tears."

On "She Works Hard for the Money," Summer has finally found a partner for a producer: Michael Omartian, also born-again. Summer wrote or cowrote all nine songs, eight with Omartian or her husband Bruce Sudano; on her last effort with Jones, she only wrote two.

Omartian is best known for his work with Christopher Cross, but he's always brought vivid energies to his work with Christian performers. And make no mistake, his production can be as sterling and full-bodied as any in rock. "She Works Hard for The Money" is full of deft embellishments and stylish accents. Omartian has assimilated the strongest elements of Summer's past productions and tempered them with egoless restraint.

On the hit title cut, for instance, one hears Moroder's shimmeringly crisp synth washes and jackhammer power chords, and Jones' lush layers and rhythmic insistence. In Omartian's hands, these elements curl around Summer's vocals rather than overwhelming them, and she's in control all the way, biting off notes and defiantly spitting in the eyes of non-tippers everywhere.

The album reflects Summer's developing spirituality, but in subtle, and occasionally simplistic, ways. Christianity informs much of the material without quantifying it and sometimes the lyrics are vague enough to be taken on a secular level. "He's a Rebel" (not the Crystals' classic) posits Jesus as a positive Marlon Brando-James Dean type ("you may not like his looks or style/but he's faster than light and he can walk a miracle mile") and couches it in brisk, new wave contours. "Stop, Look and Listen" is a punchy praise song halfway between the Chambers Brothers and the Jacksons, complete with dipped vocals and brassy Earth, Wind and Fire-style horns.

It's evident that Summer is looking for everlasting love, not just on the spiritual level, but the physical as well. Just listen to the unfettered passion of "Love Has a Mind of Its Own," her exuberant duet with gospel singer Matthew Ward, or the sensually enveloping "I Believe (I Fell In Love)."

There are several misses on the album. "Woman," despite its raw and robust edge is a bit too much "serve and stand by your man." And "People People" works a bit too hard on the missing persons-lost sheep analogy, even to the point of providing a phone number for God (432-8360, no area code). The most engaging song on the album is "Unconditional Love," with Summer trading off vocals with the group Musical Youth. The melody is an infectious swirl of acoustic and electric Carribean rhythms. It is the eternal love of Ja, or God, that they sing about, and on the chorus in particular, Summer's voice breaks free and she shouts her words with wonderful abandon.

Diana Ross' new album, "Ross" (RCA AFL 1-4677) extends the problems of her last album: a few too many cooks in the broth. This time there are seven different writing credits on eight songs, though production duties are commandeered by ex-Steely Dan producer Gary Katz (five songs) and the gifted Ray Parker Jr. (producing two cuts that he wrote). Ross wrote and produced the final cut, "Girls," a vacuous celebration of fashion's cover girls. Donald Fagen contributes a bland ballad, "Love Will Make It All Right," while Parker's "Love or Loneliness" (also the basic theme of the album and Ross' career) is bland Lionel Ritchie once removed. And that's the pattern. There's no "Muscles" this time around.

The most promising cuts are the tightly coiled "Pieces of Ice," the Michael Jackson-ish "Up Front" (could be a dance hit) and the hooky "That's How You Start Over." But with only four songs per side, Ross has to stretch the arrangements until they fall apart.

The bottom line: Donna Summer works hard for her money; Diana Ross hardly works at all for hers.