IN 1979 Linda Ronstadt had it made. With her torchy singing on safe arrangements of sure-shot oldies and southern California soft rock, she was the queen of the mainstream. In the last three years, though, she has forsaken that comfortable position for a number of risky projects. She made a surprisingly convincing New Wave album, "Mad Love." She went another direction and acquitted herself as Mabel in the Broadway production of Gilbert & Sullivan's "Pirates of Penzance." She started and scrapped an album of '40s jazz songs. She sang at antinuclear demonstrations.

Now Ronstadt (who appears at the Capital Centre Nov. 11) has returned to the mainstream with a new album "Get Closer" (Asylum 9 60185-1). The past three years have paid off in more versatile and adventuresome vocals. Though she still isn't as accomplished a singer as her less popular colleagues -- Rosanne Cash, Bonnie Raitt, Tracy Nelson or Emmylou Harris -- Ronstadt has improved dramatically. The new album is uneven, but it is highlighted by spectacular vocal duets with James Taylor, Dolly Parton and Harris plus the gorgeous ballad, "Talk to Me of Mendocino," perhaps the finest recording of Ronstadt's career.

"Get Closer," the title song, was penned by Washington's own Jon Carroll of the Starland Vocal Band and Metro. Pushed by a nifty stop-and-go piano riff, the song is a catchy rocker that Ronstadt pushes with her new aggressiveness; instead of resting comfortably inside the melody, she claws at its edges. She shows the same evenness on a punchy version of the Exciters' 1963 hit, "Tell Him."

Five other songs on the album come from the early '60s. Ronstadt does a good job riding the heavily syncopated New Orleans beat of Lee Dorsey's 1962 "People Gonna Talk," though she's less successful with Billy Joe Royal's 1965 hit, "I Knew You When." She tries to sing this shallow song tastefully, when it needs arch melodrama. She cleans up the Knickerbockers' 1965 smash, "Lies," so much that it loses garage-band vitality.

Taylor and Ronstadt take the parts of Ike & Tina Turner's 1961 "I Think It's Gonna Work Out Fine." Pop pros, they push each other to the top of their considerable skills on this funny, funky song. Ronstadt originally recorded Smokey Stover's 1962 "Sometimes You Just Can't Win" (a country hit for George Jones in 1971) for her 1977 "Simple Dreams" album. It got left off that album but now appears as a sterling reading of an old-fashioned country weeper.

"Get Closer" also includes another salvaged old track: "My Blue Tears" from the "Queenston Trio" project (trio vocals by Ronstadt, Harris and Parton). Parton's composition, with its brilliant child-like simplicity of hand-me-down folk songs, gets a lovely rendition from a single acoustic guitar and the choir of three, who employ commendable understatement. Of the newer songs, two Jimmy Webb compositions are overly sentimental and underdeveloped musically.

The album's shining moment, though, comes on "Talk to Me of Mendocino," from the 1975 album "Kate & Anna McGarrigle" (which also included "Heart Like a Wheel"). Kate McGarrigle's exquisite song describes an imaginary homesick trip across the continent. An imaginative arrangement makes Dennis Karmazyn's cello the lead instrument, as David Grisman's mandolin and Lindsey Buckingham's accordion add background shadows. Ronstadt's carefully restrained voice follows the slow, resonant path of the cello. Gradually she opens up as she imagines flying "over the Rockies and down on into California," finally gaining a stunning vibrancy of tone.

Rosanne Cash, who appears at the Wax Museum Oct. 21, displays even smarter song selection and even richer singing than Ronstadt on Cash's third American album, "Somewhere in the Stars" (Columbia FC 37570). Produced by her husband, Rodney Crowell, Cash's album presents a new, strong image for women in country music. It also presents Cash singing with a larger range and greater emotional nuance than ever before.

In contrast to the usual victim role for country women, Cash sings John Hiatt's "It Hasn't Happened Yet" as a proud boast to an ex-lover that she's getting along quite well, thank you. Her voice coasts through the songs' slow, confident soul groove with a tone as beefy and brainy as the tenor saxophone behind her. She resuscitates the Amazing Rhythm Aces' shopworn "Third Rate Romance" by balancing its lustiness with an ironic sadness. Susanna Clark's "Oh Yes, I Can" is a woman's defiant crow that she'll make it on her own; Cash romps through it with rock 'n' roll sass.

Rosanne Cash's father, Johnny, joins her on the old-fashioned "That's How I Got to Memphis." The album's first single, Crowell's "Ain't No Money," skillfully cuts open the pressure point that balances a private family life with a public career. The same theme surfaces in the first songwriting collaboration by Cash and Crowell: "Lookin' for a Corner (to Back My Heart Into)." The album ends with the title cut, Cash's own love song. Her newly mature voice rises and spreads triumphantly till it finds its home "Somewhere in the Stars."