THE SINGING '60s are back -- this week. Judy Collins, Joan Baez and Peter, Paul & Mary all appear at Wolf Trap, and -- coincidence? -- all have new LPs on the folkie-revival Gold Castle label. The singers have maintained and refined their distinctly different styles, but the albums seem unified -- as though to prove that that decade's optimism and commitment isn't lost, just tempered with realism.

On "Trust Your Heart," Collins selects 10 songs with distinct spiritual overtones, most notably a remake of "Amazing Grace," a hit for her in 1971. Collins improves on it -- her cool voice sounds stronger and purer than ever. The singer also essays the William Blake hymn "Jerusalem," with orchestra and choir, and a pair of Broadway tunes, a liltingly Latin "Day by Day" from "Godspell," and a glowing version of Rupert Holmes' "Moonfall" from "The Mystery of Edwin Drood," which could be another "Send in the Clowns" for her. Her staid, reserved covers of "The Rose" and "Morning Has Broken," both hits for other artists, are fine, but seem uncharacteristically safe.

The jacket of Peter, Paul & Mary's "No Easy Walk to Freedom" features a photo of them being arrested at the South African embassy, and on vinyl the trio comment plangently on apartheid and other world troubles in their trademark cheery harmonies. But the sturdiest tracks are two 1972 Yarrow songs, the sunny album-opener "Weave Me the Sunshine" and the melancholy ecological warning "Greenwood." You wouldn't buy this for the individual voices -- the weathering is most apparent in the solos -- but the harmonies, supported by crisp acoustic textures, sound reassuringly familiar.

Ever the camp-follower, Baez also makes reference to South Africa's woes on her most recent "Recently." You never need a lyric sheet with a Baez record -- her diction is precise -- but she supplies one anyway, so you can sing along to Johnny Clegg's "Asimbonanga" and Peter Gabriel's stirring set-closer "Biko," which she dresses up with bagpipes. The centerpiece is a concert version of the traditional "Let Us Break Bread Together/Freedom," followed by U2's "MLK," anoblique tribute to Martin Luther King Jr. But Baez, who sounds warmer and more relaxed these days, is clearly keeping her commercial options open, too -- the LP's opening bid for the CD crowd is a credible cover of Dire Straits' "Brothers in Arms."

PETER, PAUL & MARY -- "No Easy Walk to Freedom" (Gold Castle 171-001). Appearing Friday at Wolf Trap.

JUDY COLLINS -- "Trust Your Heart" (Gold Castle 171-002). Appearing Saturday at Wolf Trap.

JOAN BAEZ -- "Recently" (Gold Castle 171-004). Appearing Monday with the Smothers Brothers at Wolf Trap.