NEW YORK -- Joni Mitchell's surprise Nov. 6 performance at Greenwich Village club the Fez -- her first gig before a paying audience here in well over a decade -- proved as memorable as it was historic. Particularly because she'd been privately contemplating bowing out of live music altogether.

The show, which was only firmed up that morning and promoted via a single announcement on triple-A station WFUV overfilled the intimate 200-person capacity room. Rapt fans included Carly Simon, Eric Andersen, Victoria Williams, Natalie Merchant, and Mare Cohn, not to mention a loudly enthusiastic Chrissie Hynde ("Thank you for staying with us, Joni!" she shouted out at one point), whose Nov. 4 acoustic show with the Pretenders at the Beacon Theatre had been attended by Mitchell.

Mitchell was in New York at the request of People for the American Way, whose Nov. 5 benefit honoring cartoonist Garry Trudeau at the Waldorf-Astoria featured a short Mitchell set. There, and at the Fez, she was accompanied solely by Daniel Lanois/Joshua Redman drummer Brian Blade, whom she had first seen at last spring's New Orleans Jazz & Heritage Festival.

The New Orleans event was the most recent concert appearance by Mitchell, whose performances have become few and far between.

One likely reason for her absence, as she pointed out during the Fez set, is that she employs 30-50 guitar tunings for her complex repertoire, necessitating "endless retunings plus an army of extra guitars I had to bring on the road in what had become a truly exhausting process."

At the Fez, though, she brought out one forest-green solid-body electric guitar that plugs into an electronic tuning device, allowing instant retuning and negating the need for additional instruments.

Her pairing with Blade proved uniquely effective. The two instrumentalists, despite their newness together, interplayed with a knowing sense of intuition.

"The truth is it had been my intention to quit music right about the time I appeared last April at the New Orleans Jazz & Heritage Festival," Mitchell told Billboard in an exclusive interview two days after the show. "That appearance was to be my swan song, until two things conspired to keep me in the business. First, I heard about Brian, this great drummer from Shreveport, La., who wanted to play with me, and then Fred Walecki at Westwood Music in Los Angeles built me a prototype of this modified Stratocaster that hooks up to a digital Roland VG8 unit. The VG8 is basically a computerized brain with foot pedals into which are programmed a whole palette of sounds plus more than 30 songs' worth of intricate tunings for the night at the Fez.

"This device has the capacity to hold all my tunings of all my songs, and what the audience basically heard at the Fez show was an impromptu first live rehearsal jam between Brian and me. Happily, it turned out to be one of the highlights of my entire career, not including," she added with a laugh, "some of the wild experiences I may have slept through or blotted out from the '60s."

Mitchell delivered five songs -- about a third of the set -- from her current Reprise album, "Turbulent Indigo"; a new tune tentatively titled "Love Puts On a New Face"; and such quintessential Mitchell classics as "Hejira."

In return, she was serenaded with "Happy Birthday" by a crowd cognizant of her birthday Nov. 7.

"I won't have to say I'm 51 1/2 anymore!" joked Mitchell, looking nowhere near that age. But by the show's end, much of the house was visibly moved by the rare and unexpected experience, which was a harbinger, perhaps, of Mitchell's renewed emphasis on live performance.

"It's a whole new ballgame now for me," Mitchell told Billboard, "but it had to be, because I couldn't have gone on, considering the difficulties I was facing in getting the right quality of sound and presentation -- I needed that level of delight again. Working in this duo form with a drummer as talented and melodic as Brian is a brandnew musical romance for me, and one like a very few I've had in my career, so we're aiming to do more club appearances fairly soon in places like the Fez and the Viper Room in L.A.

"I almost canceled the Fez show just hours before I went on, maybe fearing it wouldn't work out. But happily there were no boos when I plugged in my electric guitar instead of playing an acoustic. Actually, the Roland brain provides a sound beautifully suited to each song -- like, for instance, the nylon-string tonality people are used to on certain things. You also hear a freshness and distinctiveness that's almost orchestral it's so rich. I wanted to blow chords up in size the way Georgia O'Keefe blew up the flowers in her paintings, and now that's possible."

Mitchell added that she's writing new songs and has a host of surprises planned between now and the end of 1996. But she noted that her next Manhattan appearance will not be until Dec. 6, when she attends the Billboard Music Awards telecast at the New York Coliseum to accept the Century Award, Billboard's highest honor for distinguished creative achievement.