Old folkies never die. They just get mercilessly mocked by Christopher Guest and company.

``A Mighty Wind'' is a breath _ make that gust _ of fresh air, a smart, rollicking spoof. Rounding up collaborators from his past ``mockumentaries'' ``Waiting for Guffman'' and ``Best in Show,'' director Guest spins the story of three '60s folk-music groups reuniting at a memorial concert.

Fans of Rob Reiner's ``This Is Spinal Tap,'' which starred Guest, Michael McKean and Harry Shearer as the world's loudest band of minimal-talent heavy-metal players, will treasure seeing the three reunited as another group of musical has-beens clinging to perceived past glory.

Guest again teamed with writing partner Eugene Levy to develop an overview of the main plot and characters. When it came to shooting, it was up to them and the rest of their whipsmart cast to improvise the dialogue, simulating the energy and serendipity of documentary filmmaking.

From dozens of hours of footage, Guest stitched together a deadpan hilarious portrait of these lovable, laughable people who take themselves and their calling far too seriously.

The story opens with the death of legendary folk promoter Irving Steinbloom. For a concert in his father's honor, Jonathan Steinbloom (Bob Balaban) rounds up Irving's three biggest acts, which disbanded decades earlier.

The Folksmen (Guest, McKean and Shearer) were a trio that never quite made it, scoring a modest hit with the goofy single ``Old Joe's Place'' before fading to a low-rent record label that required listeners to punch their own holes in the center of the vinyl.

The perky, folk-pop Main Street Singers were a New Christy Minstrels-type band formed from four- and five-member groups that merged to pioneer the ``neuftet'' sound. The band has been reborn as the New Main Street Singers, led by husband-and-wife folk flakes Terry and Laurie Bohner (John Michael Higgins and Jane Lynch) and featuring Sissy Knox (Parker Posey), whose father was in the original group.

Then there's Mitch & Mickey (Levy and Catherine O'Hara), an Ian & Sylvia-esque duo who were once the lovey-doveys of the folk world before their marriage tanked. Mickey's now married to a model train enthusiast who sells catheters, while Mitch has been left a glum, spacy little man fresh from the nuthouse, whose brief solo career included the tunes ``If I Had a Gun'' and ``May She Rot in Hell.''

Fred Willard, Ed Begley Jr., Jennifer Coolidge and Larry Wilson draw huge laughs from small parts. Willard, the joyously idiotic dog commentator from ``Best in Show,'' plays another overbearing fool as manager of the New Main Street Singers, a man who never had a bad idea he didn't articulate.

Begley's a TV exec overseeing the live broadcast of the concert, a Swedish immigrant who incongruously launches into torrents of Yiddish chatter.

Coolidge and Wilson are incompetent publicists, Coolidge armed with an accent ``Star Trek'' producers should study; it's so weird, it would make a great speech style for an alien species.

Every member of the cast is pitch-perfect, the characters coming off as not-that-far-off-the-mark human beings, albeit rather pathetic ones.

The goal is laughs, but ``A Mighty Wind'' manages touching moments of pathos and kinship in the interrelationships and the music itself.

Levy and O'Hara, longtime collaborators from their days on the satiric ``SCTV'' television series, bring such a sense of sweetly sad familiarity to Mitch and Mickey that their scenes at times feel like peeks into a real and painful reunion of ex-lovers.

Guest, McKean, Shearer and Levy wrote the bulk of the songs, which are toe-tappingly tuneful now and then and no more ridiculous than a lot of outdated '60s folk music sounds today.

``A Mighty Wind,'' a Warner Bros. release, is rated PG-13 for sex-related humor. Running time: 92 minutes. Three and a half stars out of four.

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Motion Picture Association of America rating definitions:

G _ General audiences. All ages admitted.

PG _ Parental guidance suggested. Some material may not be suitable for children.

PG-13 _ Special parental guidance strongly suggested for children under 13. Some material may be inappropriate for young children.

R _ Restricted. Under 17 requires accompanying parent or adult guardian.

NC-17 _ No one under 17 admitted.