NEW YORK -- If Linda Ronstadt were a police lineup, she might have trouble identifying herself.

Over 20 years of escalating stardom marked by 40 million records sold, Ronstadt has been a folk-rocker, a country-rocker, a mainstream rocker (West Coast School), a nouvelle waver, a light opera inge'nue, a sultry torch singer and a country roots singer ("Trio," her collaboration with Dolly Parton and Emmylou Harris, is up for a best album Grammy tonight, while "Somewhere Out There," her pop duet with James Ingram, is up for record of the year). She's done so many about-faces you'd think she'd be dizzy by now.

Little wonder that professional cynics and industry-ites for whom the only safe progression is I-IV-V scoffed late last year when she released "Canciones de mi Padre (Songs From My Father)," a collection of Mexican folk music drawn from the mariachi and ranchera traditions of the '30s and '40s. They saw it as just another wrinkle in the fabric of the 41-year-old singer's seemingly compulsive eclecticism.

In fact, Ronstadt was going home.

Her surname is German but she was raised in Tucson, in a family dominated by Mexican culture. Her father's family were ranchers from the Mexican state of Sonora who had moved to Arizona early this century, and her father had always sung and championed the traditional music. Linda and her sister and two brothers grew up to the strains of the rancheras (cowboy songs), corridos (story songs) and the evocative huapangos, so "Canciones" was both a recognition of cultural roots and what she has called "an act of memory."

It's an act that has inspired the most elaborate stage show in Ronstadt's career. The "Canciones" tour, which opens a four-night stand at the Warner Theatre tonight, is a festive spectacle featuring the 13-piece Mariachi Vargas de Tecalitlan, the Ballet Folklo'rico de la Fonda, dancers Sal Lopez and Urbanie Lucero and singer and guitarist Daniel Valdez. Some major theatrical talent helped put the show together, including Jules Fisher (lighting), Tony Walton (set designs) and Michael Smuin (the former director and choreographer of the San Francisco Ballet, who reprised those roles for "Canciones"). For those who don't speak Spanish, there are surtitles, just like at the opera.

"I've always had very bad stage fright," Ronstadt says on a day off between her New York concerts and the Warner engagement. "Always. But I never get stage fright when I play with them because I feel like I'm playing in my back yard. I know what I'm doing and I don't worry about it. The worst stage fright I ever got was with rock 'n' roll."

Rock 'n' roll? Gee, that seems so ... long ago.

Talk to Ronstadt for a while and you get the feeling she's not particularly anxious to reactivate those memories. Everything else -- and there's a lot of else in her future -- elicits enthusiasm, energizes her. Rock 'n' roll provokes a wrinkled nose. And the more she talks about growing up, the more it becomes apparent that rock was the only real musical departure she ever made.

"Growing up, I knew what {mariachi music} sounded like," she says. "I had that background of the authentic sound. That was easier than learning rock 'n' roll. I know that sounds weird but I understand those rhythms more instinctively than I understand blues rhythms. I never heard a blues until I was 8 years old, but I heard Mexican music from when I was a little bitty baby. And I heard classical music and opera and operetta and all those standards. But I never heard a blues until I was a big old conscious person speaking English."

Ronstadt's only been up about half an hour and she's still shaking the sleep out of her voice, but her thoughts are already racing. It's taken a decade to overcome some of the impressions made when she was a frequent Rolling Stone cover girl, usually dressed in a slip or something else more revealing than her interviews. The bimbo look fed her lightweight image, but in fact Ronstadt is intelligent and restlessly inquisitive. Offstage and offcamera, at least, she acts more like a neighbor than a star. Right now she's in a large, loose yellow nightshirt and white sweats, nibbling at a danish. No more cheesecake for Linda Ronstadt.

"Canciones" has been in the works for a decade and in Ronstadt's thoughts for two, ever since her first hit with the Stone Poneys (1967's "Different Drum"). She'd tried to interest that band in doing a Mexican folk song, but it had proved too difficult ("unless you grew up in that tradition you can't get those rhythms, they're too hard," she says). And in a Hit Parade interview at the time, Ronstadt probably surprised some folks when she said her dream was to be the world's greatest Mexican singer, following in the footsteps of Lola Beltran, the Edith Piaf of Mexico. Hit Parade misspelled Beltran's name, offering a preview of the indifference that would greet Ronstadt's occasional attempts to record a Spanish album.

In 1976, when "Heart Like a Wheel" thrust her into the rock mainstream, Ronstadt tried to talk her record company into the project. "They said, 'You've had one big hit record, don't mess with success.' " Joan Baez, she says, "had a record out in Spanish at that time and it didn't sell," therefore it followed that no Spanish album was going to sell. "So on the next record {'Hasten Down the Wind'}, I recorded a song I wrote with my bass player and my father, half in Spanish and half in English. It was a pop song so it fit in, but I was desperately trying to work in Spanish."

Soon afterward, Ronstadt had one of her biggest hits with a cover of Roy Orbison's "Blue Bayou," and she recorded a Spanish version that became a huge hit in Mexico and parts of Latin America. "It gave me a platform," she says. "In concert I sang half and half, just so I could keep the language going a little bit."

For a spell in the late '70s, Ronstadt was the top female rocker in America, with multiplatinum proof that she had finally made the right choices in songs and producers. She could have kept West Coasting along, but she was already getting restless, feeling limited by rock. The result: lead roles on Broadway in Gilbert and Sullivan's "Pirates of Penzance" and Puccini's "La Bohe'me" (reviews were mixed) and the first of three albums of lushly orchestrated standards with Nelson Riddle.

" 'Mad Love' was the best I ever developed my rock 'n' roll phrasing," Ronstadt says of her last rock album. "One of the reasons I started singing the standards was because I wanted to learn better phrasing, I thought I was weak in that place in my singing. As soon as I started singing standards, I began to realize that there's this whole vast field of vocal music that I was being shut out of by locking myself into rock 'n' roll.

"Rock 'n' roll's not vocal music. It's posing music, it's guitar music, it's bass and drums music. It's not for singers, though there are some singers who manage to do it admirably in that genre, who have a peculiar kind of voice that can express itself that way, like Chrissie Hynde, who's an absolutely brilliant rock 'n' roll singer, or Tom Petty, whose idiosyncratic vocal properties are well served by that genre."

And so, though her record company would have preferred more of the same old sound, Ronstadt began stepping out. Her first standards album was a surprise hit, rising to No. 3 on the charts, staying on them for two years (still a personal best), selling more than 3 million copies and leading to two more albums that sold almost 6 million copies between them.

Ronstadt was doing a media make-over as well. The press had become obsessed with her relationships (with former California governor Jerry Brown and actor-director Albert Brooks in particular). Finally, Ronstadt, who had been perhaps unwisely open with journalists, began to limit her interviews to the subject of music and left the rest to speculation. (For some time now, speculation has centered on movie mogul George Lucas, who happens to be testifying on the Hill tomorrow about the rights of artists.)

"I wasn't so much compulsively open," she explains, "it's that people just wrote whatever they pleased. A great deal of what they wrote didn't have any basis in fact whatsoever, so there were torrents of strange misinformation from old interviews, which were then carried forward."

Around the time she began taking musical risks, she disappeared as a Rolling Stone cover girl -- a loss she's not bemoaning. After a flare-up over the magazine's use of what Ronstadt says was an unauthorized (and decidedly overfleshy) photo by Annie Leibovitz, she recalls, "I decided I didn't care about what was hip and what was trendy and what was going to sell, because by that time I'd accumulated a great deal of money from making records. All I cared about was, was I having fun singing or was I going to be bored? So I decided to have fun singing and I have never looked back."

If Ronstadt has paid little attention to the musical borders that rule pop culture, it's an attitude rooted in her Southwestern upbringing. She likes to point out that the Sonora Desert contains both Arizona and the Mexican state of Sonora, that "the border was an arbitrary line. My family were ranchers and they'd been ranchers since the 1500s, had lived in that area since then. They were stable; the border was not. The border moved with the Gadsden Purchase in the middle 1800s. My great-grandfather, who gave me my German surname, arrived at the beginning of the 19th century as a mining engineer and married into a family that had been there forever."

Ronstadt's musical heritage dates back at least to her grandfather, who played the flute and led a band in the 1880s. "He did arrangements of the songs of the day, even of the 'Pirates of Penzance,' " she says. "I have a cornet part in his handwriting dated 1896, so even this music is not new for us."

She absorbed mariachi music from her father (who ran a hardware store, and one of whose paintings is the back cover of "Canciones") and her two brothers (one is now Tucson's police chief; both appeared on the record). Despite its familiarity, however, reconnecting with it as a recording artist took some doing.

"I really wanted to meet some mariachis but they were hard to find, because it's an old tradition and not as prevalent as it was in the '40s and '50s. The really great mariachis stay in Mexico," she explains, while the substantially different norteno style is more prevalent north of the border. "But that was not what I learned from my father and from my trips to Mexico when I used to follow them around in the streets. If you were a woman you couldn't go into a bar, and certainly not if you were a little girl. But I used to stand outside the door and listen. I used to stare at the guitarron player and think, 'What the hell is that rhythm he's playing?' "

Also, as a rock star, Ronstadt understood it would be difficult to learn the music because she might be seen as a dilettante. What saved her was the start of an international mariachi festival in Tucson three years ago. The organizers invited her to sing for a benefit concert and she agreed -- provided that "they introduced me to Ruben Fuentes, who composes and arranges for Mariachi Vargas, and that they would have him do the arrangements for me. It was an opportunity to meet him and get my feet wet a little bit and then approach him about helping me with the recording project -- if he felt encouraged by what he saw."

Mariachi Vargas is widely considered the world's greatest mariachi orchestra and Fuentes, who did the arrangements and conducted on the "Canciones" album and tour, is one of the great forces in the music. He would become Ronstadt's mentor in much the way Nelson Riddle had -- but ironically, pupil had to coax master back toward his own roots.

"What he wanted to do is to push the mariachi orchestras more into the areas that Nelson had already established, playing some modern chords besides roots, thirds, fifths and sevenths; once in a while there'd be some sixth or ninths in there and I'd just hit the ceiling ... I wanted it to sound like it was before World War II.

"And he agreed and came back with these very modern arrangements that were so flashy," Ronstadt continues with a laugh, "because he'd been working in movies for years. He had basically established the style in the '40s, defined it, brought it up to standards and then he started branching out, doing 300 movies scores. So the stuff sounded very cinematic and I didn't want that."

The negotiations were complicated by ethnicity. "Women have a lot of power in {Mexican} culture," Ronstadt says, "but they do it in a certain way, and where my culture is Mexican, my mother is Dutch. Ruben used to say to me, 'You're like a Dutch, so straightforward.' Whereas Mexican thinking is very oriental because it's very Indian. Mexico is the land of magic, not of logic."

Ronstadt, who says she worked harder on this project than any she's ever done, went to Mexico for some intensive language study. She was somewhat bilingual growing up but "it was taken away from us when I went to school, where they actively discouraged anybody speaking Spanish."

She also had to relearn the rhythmic codes, how to count the lines (by following the bass lines), accent a line, effect certain pronunciations. "Sometimes, people think it's out of tune," she says. "That's so bizarre because the music is so amazing. It's on another scale, not like a Western scale ... the way the violins relate to each other and the way the bass speaks ... the overall mix of instruments ... the way the vihuella speaks and takes the place of the drums. The tuning is tempered all the time, and so are the harmonies; they're wonderful, it's like Mexican bluegrass. It's not this rigid, European, classical pitch."

The music, she adds, "has all the resonance of the Indian culture ... the Spaniards found that the Indians sang beautifully and had highly developed vocal traditions and instrumentals, so that's been incorporated into the musical body of the conquering nation and this rich, wonderful, tormented, anguished cry that became Mexican music."

Ronstadt loves working in an ancient tradition. "We don't have any tradition in contemporary music except change," she says. "Mutate, like a virus. And there is something so edifying and so grounding in being able to allow all those generations of people to sing through you, because that's really what it is ... Generations of people have refined this music so that it is a very distilled essence of speaking one emotion or another, just like classical music is, or classical dance."

Since it came out in November, "Canciones de mi Padre" has sold more than 500,000 copies (85,000 was the break-even point), which should buy Ronstadt the freedom to continue her eclectic course. Her record company "has been very good about this," she says. "But if I make a record that doesn't sell, they're not going to encourage me to make another one like that, so I've been very lucky."

Elektra might want a return to mainstream rock, preferably in English, but Ronstadt has other ideas. First, she'll probably be doing an album with Aaron Neville, the astounding lead singer of New Orleans' Neville Brothers. "We like to sing together," she exults. "I just like to stand there and look at him, he's so gorgeous. He's fabulous.

"The reason that New Orleans is great, and why I love this Mexican music, is that it's regional. Each song sounds exactly like where it came from and no other place. Regionalism has been destroyed in this culture, and is soon to be destroyed all over the world, because first television made everything homogenous, and now radio -- because it's programmed by these corporate pinheads who take 'market surveys' ..."

Another project is "Voces" (Voices), written especially for Ronstadt by jazz trombonist Barry Rodgers. It will incorporate Afro-Cuban cultural traditions, she says, to tell the story of "a second- or third-generation Latin girl living in a stupid shopping mall culture, buying shoes, buying cars. She works two jobs, her husband works and is too tired to do anything but watch television, she's got kids she's raising in this culture and she's remembering the Latin culture that she came from and thinking, 'What have I left behind me?' -- trying to figure out what she can salvage from that and how she can apply it to her own life. It sounds kind of serious but it's also very funny and it floats back and forth between English and Spanish because she's a bicultural, bilingual person."

"Voces" was originally conceived as a video project, but Ronstadt says that "to sit down and make a video, put on all that makeup, do your hair 29 times a day, it's not very appealing to me. I don't like to change clothes that much." She's rather do a foto novela -- one of the soap opera comics with photos instead of drawings that are very popular in Latin America.

Future chart appearances could come from anywhere. Her duet with Paul Simon, "Under African Skies," was recently released as a single. She was on Philip Glass' "Songs From Liquid Sky" project; she's singing backup on the new Toto album; the "Trio" album is still doing well. Who knows, maybe she'll sing the theme to "Howard the Duck II" (just kidding).

She's also produced her first album, for multi-instrumental wizard David Lindley, a long-time friend and former bandmate who turns out to be a relative "through the Spanish California side."

So these are good days for Ronstadt. She seems animated by what she's doing and what she's planning. "My voice is stronger and I have an infinitely better understanding of rhythm," she says. Then, laughing: "After trying to understand the huapangos, I understand rhythm much better."

What's more, she says, "I think I have a better idea of where I stand as a singer. I mean, I know that I'm a good singer. I don't think, and I don't think I'll ever think, that I'm a truly great singer. Those people are very rare. There are a handful of really great singers in the world, Lola Beltran is one of them. Billie Holiday and Ella Fitzgerald are really great singers. I don't think it's anything that you can aspire to."

She doesn't mention Lotte Lenya. And despite her family's German side, there's no album of lieder in the works.

"I've read Goethe and I like Beethoven and Bach and Hegel's a good philosopher and all that stuff," Ronstadt says with a smile, "but I'm not very connected with German culture."