ELLIE Greenwich is a rock 'n' roll Renaissance woman.

In her 20-year career, she's done it all: written more than a dozen Number One pop classics, sung doo-wop background vocals with groups from the Crystals to Blondie, worked with landmark rock producers such as Phil Spector, Lieber and Stoller and Shadow Morton, discovered many recording artists, including Neil Diamond, and written and sung countless commercial jingles. And she's still doing it. So why doesn't anyone know her name?

"I was very happy being behind the scenes," says Greenwich, in a telephone interview from her Manhattan apartment, in a wisecracking voice that reveals her Brooklyn roots. Greenwich got her start in the pop/rock business as a demo singer and piano player with Lieber and Stoller.

With ex-husband Jeff Barry (who went on to produce the Archies) and others, Greenwich co-wrote some of pop's most memorable hits, including "Leader of the Pack," "Be My Baby," "Chapel of Love," "Da Doo Run Run" and "Doo Wah Ditty."

"You have to find the right person to write with," Greenwich says. "If it's not right, if you're not on the same wave length, it's torture! It's like a married couple--you start driving each other crazy."

One of Greenwich's recent songs, "Keep It Confidential," written with rock singer Ellen Foley, is rapidly ascending the pop and black charts as interpreted by former Labelle singer Nona Hendryx, who has put a decidedly rhythm-and-blues spin on Greenwich's straightforward pop-and-roll tune. "This is the time when you work with the artist," says Greenwich, who gets calls from singers such as Pat Benatar and the Pointer Sisters, asking her to write songs tailored to them.

Greenwich, who says her "roots are loving the girl groups," says she is continually surprised and sometimes delighted when she hears a new version of one of her songs. "I find it wild that a song can last and can be treated in so many different ways by so many people. Like, Fonzi Thornton one of Chic's background singers just covered 'Be My Baby,' which he made real danceable.

"Of course, it's heartbreaking when you hear your song done completely wrong, and you say 'God, what have they done to my song,' like pop singer Melanie said. But music is all interpretation."

"It's funny what happens when you take a song from my ' '60s head' and mix it with new wave or whatever," says Greenwich. She used to hammer out her songs on the piano, but now finds it easier to sculpt a song using electronic technology, such as the synthesized Linn Drum kit she has in her self-built eight-track studio at her apartment. Greenwich says she'd like to do a "real heavy-synthesized dance version" of "Do Wah Ditty" soon, featuring her own singing.

She has recorded two albums of her own. Although both sank without a trace in America, one did well in Europe. "When heavy metal came in in the '70s, my songs didn't fit," says Greenwich, explaining why her career took a turn from Tin Pan Alley onto Madison Avenue. "Most of the bands were self-contained anyway, so where was there room for me? I started writing jingles."

Greenwich wrote jingles for Coca Cola, Clairol and Cheerios, and Pepsi's hummable, "Come on, come on, come on" jingle, among others, and she's still writing a lot of commercials. "I have a Budweiser coming out, and a new 'Oooh la la, Sasson,' which I wrote and sang lead and background vocals on." But Greenwich says she'd like "to get back to my own songwriting, which is where it all started."

Something that should put Greenwich into the history books is her discovery of Neil Diamond. "I was called by a publisher, when I was still the 'demo queen,' to do a demo of some songs by this guy, Neil Diamond," Greenwich says. "He had written the songs, one was called 'Call Me His,' which you've never heard of, and he was starving then, the whole bit. I introduced him to Jeff Barry and said, 'You have to listen to this guy.' Neil came up to Lieber and Stoller's offices and it was funny--I liked the way he wrote, and not the way he sang. Jeff liked the way he sang, but not the way he wrote."

Greenwich was discovered at age 14 by musical director Archie Bleyer, playing her own songs on the accordion. "I still have that accordion," Greenwich laughs. "It's just sitting there in the closet, and I open the door at parties and say, 'God! Loooook at this!' Maybe I'll go back to playing it. It would be a new sound. I could get it electrified . . ."