Michael Ball, a British stage actor and singer, was watching a performance of traditional Christmas songs at a London drama school this month when the students unwrapped Joni Mitchell's 1971 song "River."

Ball says he was somewhat startled, given that "River" isn't really a Christmas song.

Never mind that its opening melody is "Jingle Bells" in a minor key and that Mitchell's lyrics begin, "It's coming on Christmas, they're cutting down trees /They're putting up reindeer, singing songs of joy and peace." Ultimately, it's a bereft song about a woman whose romance has gone bad and who wants to escape. The drama just happens to be set around the holidays.

Calling from London, Ball says: "There were all these 18- and 19-year-olds doing traditional Christmas songs, and then, bang -- they start doing 'River.' I'm thinking: Where on Earth did this come from?"

Of course, Ball might ask himself that same question: Six years ago, he recorded a version of "River" for his own holiday album, "Christmas." At the time, he thought he was a maverick for placing "River" alongside the likes of "Silent Night" and "Have Yourself a Merry Little Christmas."

As it turns out, though, plenty of artists have been dreaming of a blue Christmas over the past decade, as Mitchell's song -- originally featured on the not-exactly-festive album "Blue" -- has somehow become a seasonal favorite.

"River" has long been a popular cover among musicians, more than 100 of whom have recorded it for commercial release. But since smooth-jazz guitarist Peter White featured "River" on his 1997 holiday set, "Songs of the Season," the tune has been included on more than two dozen Christmas albums. This year alone, it's appeared on at least seven new seasonal discs, from Sarah McLachlan's Grammy-nominated "Wintersong" to "James Taylor at Christmas."

"I don't know why it's suddenly getting picked up as a Christmas song," Taylor says. "But some things just become identified as seasonal songs, and this is now one of them."

Taylor knows "River" well, having first heard it when Mitchell played it at her home in Los Angeles.

"I've known it from the time it was written, and I've always loved it," he says.

When he finally decided to record a Christmas album, he decided to include "River" alongside various seasonal staples. "Most Christmas songs are light and shallow, but 'River' is a sad song," he says. "It starts with a description of a commercially produced version of Christmas in Los Angeles . . . then juxtaposes it with this frozen river, which says, 'Christmas here is bringing me down.' It only mentions Christmas in the first verse. Then it's, 'Oh, I wish I had a river I could skate away on' -- wanting to fall into this landscape that she remembers.

"It's such a beautiful thing, to turn away from the commercial mayhem that Christmas becomes and just breathe in some pine needles. It's a really blue song."

Which is exactly why Ball recorded it.

"I'm not a big fan of Christmas, and I think there are a lot of people who feel a bit melancholy at the holiday," Ball says. "We've all sort of been there: It's coming on Christmas, all that preparation is going on, and you just want to escape. You don't want to buy into it. It's a time of year that brings up a lot of memories for people, and if you're missing somebody, it's hardest at this time of year."

In some ways, it's the perfect anti-Christmas song, running counter to the prevailing seasonal spirit. And yet, various versions of "River" have become hits on the more than 400 radio stations that are playing Christmas music and nothing else through the holiday, making Mitchell's tune one of the rare "new" entries in the Christmas canon. Another rare, recent exception: Mariah Carey's "All I Want for Christmas Is You," written in 1994 with Walter Afanasieff. But Carey and Afanasieff wrote that song hoping it would become a holiday hit. Not so for Mitchell and "River."

Or so we think. Mitchell herself has been unavailable to comment for this story over the past three months. (The publicist for the famously reclusive artist says there's a good reason: Mitchell has sealed herself off while finishing a project with the Alberta Ballet, "Dancing Joni: The Fiddle & the Drum.")

Mitchell's old friend Linda Ronstadt says the "River" author probably hasn't paid much attention to the song's newfound status.

"She always has her eyes on the future and doesn't really look back," Ronstadt says. "And like anybody who creates things, Joni doesn't do it for applause. But I do think you're always a little bit happy if somebody likes what you're doing."

If Mitchell never intended to write a Christmas hit, she'd hardly be the first songwriter to find accidental seasonal success. Ace Collins, the author of "Stories Behind the Best-Loved Songs of Christmas," notes that several songs now considered Christmas classics weren't actually intended for the holiday. The most famous is "Jingle Bells," which was written by one James Pierpoint for a Thanksgiving program at his Unitarian church in the 1850s.

Ann Kline, music co-supervisor for the NBC drama "E.R.," is just happy to have "River" at her avail. Kline hadn't thought of it as a seasonal song before this year, but she wound up using McLachlan's ethereal version on the recent holiday episode of "E.R." (It wasn't exactly a happy, feel-good program.)

"As much as we struggle to find different Christmas songs -- things that aren't 'Let it snow, let it snow, let it snow' -- I'm sure artists go through the same thing when they're making holiday albums," she says. "There are only so many Christmas songs out there."

Ronstadt said "River" was an obvious choice when she recorded her holiday album, "A Merry Little Christmas," in 2000. "I'd wanted to record it for years, and I just couldn't figure out where to put it," she says. "I'd never heard it in the context of other Christmas songs, but I always wondered why that was."

Ronstadt has never discussed the meaning of the song with Mitchell. But she has some ideas about what might have inspired it -- possibly including Mitchell's daughter, who was born in the 1960s, when the singer was 21 and about to move from Saskatoon to Toronto. Mitchell gave the child up for adoption and didn't have any contact with her until 1997.

"I think that's what a lot of her singing is about, because it has this very sad tinge," Ronstadt says. "But who really knows if that's what 'River' is about? The answer is: I don't know, and I bet Joni doesn't, either."

Taylor, however, says the song is most likely autobiographical, given that "it starts with a girl from Canada watching them try to make Christmas on La Brea in Los Angeles." But he hasn't discussed the meaning with Mitchell, with whom he was romantically involved in the early 1970s.

"Do I want to know who she made cry, who she made say goodbye? Well, I haven't asked her that question," Taylor says. "That's the only mystery in it: Who was it whose heart she broke?"

With a laugh, he adds: "There were a lot of us."