THE COVER of the Pretenders' new album, "!Viva El Amor!," shows Chrissie Hynde with her trademark shag and a fist raised, revolutionary style, against a blood-red backdrop. It's a fittingly conflicted confluence of title and image -- one of rock's most distinctive voices, Hynde has always mixed punk attitude and pop craft in songs that are alternately caustic and compassionate.

That photo is one of the last taken by Linda McCartney before she succumbed to breast cancer last year. McCartney and Hyndehad been friends for 16 years, first drawn together by a shared commitment to animal rights. "That was the original bond," Hynde explains. "Linda found in me someone who really understood her animal agenda, but we had a lot in common -- we were both displaced Americans in England and we both loved Paul McCartney."

Hynde and McCartney discussed the cover concept -- "we knew exactly what we wanted with the fist in the air/struggle/propagandist looking thing. Linda was way into it and she's the one who suggested using black-and-white. Then she said, `I'll see you in a couple of weeks.' But I think she knew that wasn't going to be the case."

A couple of weeks later, Linda McCartney died in California. Not long after, an envelope arrived at Hynde's home with that final portrait and Linda McCartney's admonition to "Do anything you want with it."

Which, come to think of it, has been Hynde's approach to rock 'n' roll for the last 30 years, ever since forming her first band in Akron, Ohio, at age 17 (the brief-lived Sat.Sun.Mat. also featured future Devo-tee Mark Mothersbaugh). England, which has been Hynde's home for the last 25 years, first called in the early '70s -- a period that found Hynde slumming as a rock critic for New Musical Express and working at Malcolm McLaren's pre-Sex boutique while trying to put a band together. The later part of the '70s found her flirting with aggregations that never quite jelled -- the Loveboys with Richard Hell and Sylvain Sylvain; Big Girls' Underwear with Mick Jones, later of the Clash; and Masters of the Backside with future members of the Damned.

Finally, in 1978, Hynde teamed up with guitarist James Honeyman-Scott, bassist Pete Farndon and drummer Martin Chambers, and the Pretenders were in business. Their eponymous 1980 debut was one of the greatest in rock history, producing such classics as "Brass in Pocket," "Kid" and a cover of the Kinks' "Stop Your Sobbing." Those songs remain central to the Pretenders' repertoire, though only Hynde and Chambers remain from the original group. Honeyman-Scott died in 1982, Farndon a year later, both from drug overdoses.

As the Pretenders end their second decade -- doing some dates as part of the final Lilith Fair tour and some on their own -- Hynde insists she never envisioned her rock passion providing a career.

"I just wanted to play guitar in a rock band," she says with a small laugh. "I was trying to avoid having a career. I still have these kind of hippie values -- I wasn't too bothered about the fruits of the work, I was more interested in just doing the thing, wanting to get this band together. And, in perhaps a funny way, the demise of Pete and Jimmy has given the Pretenders a kind of longevity because I've tried to keep the music alive in honor of those guys."

It's always been on Hynde's terms, of course. Twenty years have produced only seven studio albums, a singles collection and 1995's "Isle of View," a live acoustic career retrospective with string quartet. And over the last decade and a half, Hynde has refused to be a rock 'n' roll road warrior. She didn't tour for eight years while raising her two daughters, Natalie Rae, now 16, and Yasmin, now 14 (fathered respectively by Ray Davies of the Kinks and Jim Kerr of Simple Minds).

"To me, their privacy and their childhood, their lives, that's always been priority number one," says Hynde, who two years ago married Colombian sculptor Lucho Brieva. "I'm not a workaholic -- I'm going to be 48 years old, my kids are teenagers now . . . I've got a civilian life."

Music, she explains, "is my work and it's important to me, and every night when we're onstage, I feel redeemed by it -- it's a wonderful thing. But I've got other interests in my life that have nothing to do with this."

So much so that Hynde's daughters saw her play electrically for the first time last year when the Pretenders toured with Royal Crown Revue and the B-52s.

"Before, it was always past their bedtime," Hynde points out. "They came out for a few of the shows and it was probably a bit of a shock for them. I'd come offstage and they'd go `Oh, you were good, Mom!' "

Doing "Isle of View" allowed Hynde to revisit the Pretenders' legacy, though she never expected to do so acoustically. "But I liked doing the songs with a string quartet and being quiet, so that was interesting, trying something I always reckoned I wouldn't do. But we're still a rock band." One that's been through many makeovers, it should be noted. Chambers, who'd left in 1984, returned a decade later, joined by guitarist Adam Seymour and bassist Andy Hobson. That lineup's now been together longer than the original one.

The "Isle of View" experience did open Hynde up enough that she begins an upcoming VH-1 "Storyteller" show acoustically. "I wouldn't have done that in the past. In fact, I was laughing because I was sitting down looking over at Adam thinking, what if we were just in some New York coffee bar and the band had left us? Well, I'm much happier with the band!"

Hynde, who toyed with the coffee house singer routine in a "Friends" episode that found her competing with Lisa Kudrow's Phoebe character, pays tribute to the '60s Greenwich Village folk scene on the new "Bleecker Street" tribute album, covering Tim Buckley's gorgeous ballad "Morning Glory." She's also heard performing "She" on a new Gram Parsons tribute album produced by Emmylou Harris, who duets with Hynde on the track.

As might be expected, the Pretenders have been spicing up their Lilith Fair dates. "We're a rock band, so that's just what the doctor ordered for the tour," Hynde says mischievously. "It's nice to be a bit flowy and soft and gentle and everything, but it's also nice to stand up and rock out."

And to cause trouble every once in a while. At a show a few days ago, Hynde explains, she, Bonnie Raitt, Sandra Bernhardt, Sheryl Crow, Beth Orton and members of Luscious Jackson gathered backstage and decided to sabotage the finale. "We walked out and said to Sarah [McLachlan], no, we're not doing the song that she had planned. We told the band to stop playing and went into this a capella version of Karen Carpenter's `Superstar. . . '

"And Sarah loved it! She got straight into it and the band picked it up and it sounded like it was completely rehearsed! That was real fun that there could be a moment of dissent, but Sarah's really game."

THE PRETENDERS -- Appearing Wednesday as part of Lilith Fair at Merriweather Post Pavilion with Sarah McLachlan, the Dixie Chicks, Sheryl Crow, Me'shell N'degeocello, Kendall Payne, Medieval Babes, Cherokee and others. * To hear a free Sound Bite from "!Viva El Amor!," call 202/334-9000 and press 8112. (Prince William residents, call 690-4110.)

CAPTION: Chrissie Hynde appears Wednesday at Lilith Fair in Columbia.