In the event you've lived the past year on a musical diet consisting only of heavy metal and rap, you probably missed the fact folk music is enjoying a healthy revival.

Its been decades since so many talented songwriters have had so much to say and have said it so well. And through the persistent efforts of veterans like Nanci Griffith, John Mellencamp and Bob Dylan, folk continues to worm its way into the mainstream of American pop, rock and country music.And most folks probably don't even realize how prevalent it has become. Most recently, there is Bette Midler's lovely rendition of Julie Gold's "From a Distance" - a standard on the folk music circuit for years that went Top 5 on the Billboard charts. And then there is folkie Mary Chapin Carpenter winning country music awards right and left.

To top that off, some of the biggest names in rock 'n' roll have been digging into the past to revive musical treasures by the likes of Woodie Guthrie and Robert Johnson.

What during the 1960s became a strictly defined musical genre restricted to political activism has now become a multi-visioned vehicle for songwriters to explore everything from family relationships to social commentary to world problems of poverty, war and the environment.

And that has allowed a whole stable of great new songwriters like James McMurtry, Darden Smith and others to use acoustic folk influences to expand the horizons of popular music. And in the process, "old" veterans, like Peter, Paul and Mary, Joan Baez, John Hiatt and Emmylou Harris have recently put out some of their best music in years.

Peter, Paul and Mary's new "Flowers and Stones" (Gold Castle) is a good example. Acoustic tradition, beautifully harmonies and a healthy mix of original tunes and covers makes it a thoroughly delightful offering. Particularly engaging are covers of the anti-materialistic "Yuppies in the Sky," and Bob Dylan's "I Shall Be Released" and "It Ain't Me Babe."

While their recent releases have been adequate but uninspiring, this time the trio hits on just about everything with plenty of irony, politics and humor - a perfect mix for this trio.

If absence makes the heart grow fonder, then seven years since their last release is plenty of time to remind us how fond we are of Kate and Anna McGarrigle, whose "Heartbeats Accelerating" (Private Music) never skips a beat.

Keeping with the tradition of exceptionally rich vocals and lyrical relevance that have been their hallmark for 15 years, the McGarrigle Sisters unload both barrels with "Heartbeats."

A not-unpleasant surprise is the mesh of their folk roots with electronic music. But never does the electronics get in the way of the music itself, which undulates between whimsical and melancholy with remarkable ease.

Kate, who is married to folk singer-songwriter Loudon Wainwright, dips into her bag of tricks for the decidedly weird "I Eat Dinner" and the grim "Mother Mother."

Anna, on the other hand, goes more for abstract images with tunes like "Hit and Run Love." Her husband, Philippe Tartarcheff, contributes two good songs as well.

A newcomer with Dylanesque potential is Joe Henry, whose "Shuffletown" (A&M) is often brilliant, although inconsistent. Employing the throaty vocals a la Bob Dylan and Van Morrison, Henry effectively uses guitar strings and lyrical imagery to paint a colorful musical tapestry.

The imagery is often bizarre as his poetic musings wander surrealistically from a "barbership by the dead mountain" to fish singing in trees. If he can harness his poetry with a little more melody, Henry could just shuffle his way into the Big Time.

Another newcomer with awesome potential is Alison Krauss, whose "I've Got That Old Feeling" (Rounder) exudes a musical maturity far beyond her 18 years.

Particularly striking is the fiddle-player's effortless vocals, which immediately conjures up comparisons to Emmylou Harris. The subject matter - heartbreaks on the highway of love - is also similar.

Despite her age, Krauss maneuvers effortlessly through her bluegrass melancholy in a quiet, observatory sort of way that is comfortable. Particularly good are "That Makes One of Us" and "Wish I Still Had You," bluegrass tunes both dressed in a contemporary sound.

Jonathan Richman is a folk singer. And a punk rocker. And just about everything else. So on "Jonathan Goes Country" (Rounder), is Richman now going country?

Well, yes and no. As one reviewer correctly noted, "This may be a gimmick album born out of creative desperation, but it's gimmickry that works."

Richman's rodeo of the weird proves strangely endearing, especially compared to the super-slick packaging of today's country music. Which probably makes this more of a folk record with a whole lot of country flavoring.

Richman songs such as "Reno," "Since She Started to Ride," and the uniquely weird cheatin' tune "The Neighbors" are nothing short of fun. And he's also very good when he turns serious, like on Porter Wagoner's "Satisfied Mind."

While names like Krauss, Richman, Henry and the others may never become the household names they might someday deserve, they do offer an obscure treasury of new music that made 1990 one of the best - despite the combined effects of M.C. Hammer and Madonna.