He was calling from a pay phone in the McPherson Square Metro station. Seems like a natural place for a performance artist to do an interview. Incorporating the environment. Bucking the traditional PR guy and tape-recorder scene. Spewing out opinions on something as common and socially accepted as Santa Claus.

The Santa Myth. That's what David Web calls it. And he's trying to deflate it. "Santa's sort of like the last representative of the side of American culture that everyone is trying to exorcise from their lives. You know how fitness-conscious everyone has become. Well, Santa doesn't really fit into the picture we are trying to create in our culture -- slim, trim and fit.

"But," he says, assuringly, "I'm not ragging on Santa."

Web is one of a host of performance artists appearing in a six-hour showcase, "Sprocket Winter Solstice." Some of the acts will be long and complicated. Others, like Web's, will be quick hits. Web's not sure yet, because, you know, these things can change right up to the last moment, but he thinks his "Santa Myth" piece will run, oh, about two minutes, tops.

Franklin Wassmer's piece, on the other hand, is a bit more complex. Wassmer has commissioned local musical artist Mike Wingo to compose a work for four percussionists. Sounds normal enough, right? Well, here's the twist: The instruments are the big picture windows of d.c. space. "I wanted to use the environment," Wassmer says. So he has.

Sensitive microphones will be attached to the windows, so even the slightest touch will become an audible vibration. There will be three performers parading onstage, one carrying a stereo speaker that will project these percussive sounds. Another will carry a television that will project images of decorated department store windows. The third will carry a window-size sheet of glass.

Simultaneously, in the audience, there will be a group of extravagantly dressed characters, posing and strutting like fashion models on a catwalk. Their arms will be laden with oversized shopping bags containing music boxes chiming sweet, harmless tunes.

"It's something extremely elaborate for a short period of time -- 15 minutes," Wassmer says. "I like the complexity and the simplicity, how so many different elements create something relatively simple."

"Sprocket Winter Solstice" is from 8 p.m. to 2 a.m. Friday at d.c. space. Tickets are $5, and proceeds benefit the homeless in Washington. For information, call 202-347-1445. JUDY COLLINS, IN A 'BLIZZARD' Judy Collins has been a busy lady lately. She's just put out a book and cassette reading of the children's classic "Thumbelina," featuring a few songs she composed. Her song "My Father" was recently turned into a children's book. She has established the Eden Foundation, which gives grants to plant trees around the country. And she's on the road, promoting her new album "Fires of Eden" (Columbia), which contains a song she absolutely adores called "The Blizzard."

It's a long, winding song. The tinkling keyboards create the whooshing of falling snow as her lullaby voice weaves a tale of how she wandered into a diner in the mountains of Colorado and encountered someone who became, almost instantly, her confidant, her soulmate.

" 'The Blizzard' is a great story about being caught in a huge snowstorm with a stranger," says the blue-eyed songstress. "And it's a metaphor for your internal snowstorms and difficult times. I think everyone has a moment when they feel lost in a storm."

Collins primarily records others' compositions, and for the last few years hasn't done much songwriting on her own. But "The Blizzard," from beginning to end, took only 40 minutes to put down.

"It sort of poured out," she says, "like I was taking dictation. I knew what instruments would be used and everything. Writing a song is like building a house. First you have the plans, then the tools and materials. But this one was like an architect's dream. Everything was there."

However, she says, don't use this song as a map the next time you vacation in the Rockies. It came from her imagination. "And some say my geography is questionable," she says, laughing.

Judy Collins is performing at the Birchmere tomorrow night at 8 and 10. Tickets are $25 and available at TicketCenter. For information, call 703-549-5919. CITY AT 31 Although improvisation has probably existed for centuries, for the last 30 years the folks at Second City have elevated it to art -- as well as a full-time job. The Chicago-based company, which has turned out such comedic stars as John Belushi, Bill Murray, Gilda Radner, Shelley Long, Alan Arkin and Dan Aykroyd, is considered the granddaddy of contemporary improvisation. And also a springboard for new comedic talent.

"Chris Farley went to 'Saturday Night Live' this year," says producer Joyce Sloane. "Tim Meadows, in the resident company, is the next one to go. He's one to watch. And we have someone else out in California right now talking to Rob Reiner."

The success of Second City lies in its philosophy and its creative method. The young performers who attend the workshops and join the troupe are not thought of as stand-up comics, but rather comedic actors. The bulk of an SC show is a series of rehearsed routines based on improvised skits. Often after a show, the actors submit themselves to the audience's whims, improvising on random suggestions. If something works, they write it down. Shape it. Polish it. And add it to their repertoire. Improvisation is the root. Fine comedic acting is the result.

Although Second City prides itself on social satire, it's best known for its political humor.

"They do a wonderful thing about Mount Rushmore," says Sloane. Then she chants: "Four stoned guys. We can't close our eyes."

"And there's something about Texas: Two senators are debating, and in protest, the senator from Texas says, 'Texas withdraws from the United States.' And the other senator says, 'Who cares?' "

And as is traditional, the troupe closes the act with the Second City version of the Supremes: Dressed in justices robes, the performers sing "We Lean to the Right."

Second City is celebrating its 31st birthday tonight with a show at Chelsea's at 7:30. Tickets are $12. For reservations and information, call 202-298-8222.