Len's mightily infectious pop-hop single "Steal My Sunshine" helped elevate the top soundtrack of last summer, but it almost didn't make it onto the Canadian group's major-label debut, "You Can't Stop the Bum Rush."

"Sunshine," with its carefree groove and sugary he-sang, she-sang discourse, was temporarily lost in the band's Toronto home studio. The master tape accidentally slipped into the shadows, unspooled and gathering dust, until it was rescued by the Burger Pimp.

"The master was under our bed," says the Burger Pimp, a k a Marc Costanzo, Len's chief writer and producer. When Len, which performs tonight at the 9:30 club, was looking for a song to fill out the album, Costanzo and his sister/vocal foil Sharon remembered "Steal My Sunshine," which puts a '90s hip-hop twist, and a more positive spin, on Human League's new romantic discourse, "Don't You Want Me."

"Marc just dragged me out of bed and into the studio one morning and said, 'Do you want to sing on this?' " Sharon Costanzo recalls of last year's recording. "Later, he told me he was going for that Human League vibe and had always wanted a song like that, but I had no idea that's what it was about. And as soon as we recorded the song, it was done for me. We both liked it, but then I never thought about it again."

That is, until the need for a song arose.

Then it landed on the soundtrack for the teen-action film "Go." While everybody expected big things from fellow contributors No Doubt, Natalie Imbruglia and Fatboy Slim, radio instead zeroed in on "Steal My Sunshine," apparently mesmerized by its quintessential summertime beat and sing-along hook. That led to a Burger Pimp-directed video--lots of motor scooter and amusement park fun--which in turn led to a rare double breakthrough for Len (picked as an emerging act by both MTV and VH1). All that led the band's label, Work, to push up the album's release date by several months.

Neither Marc nor Sharon Costanzo, who trade off on the "Sunshine" verses, quite understand what all the fuss is about.

"We have a lot of songs like 'Sunshine,' " Marc Costanzo insists. "I'm not saying that they're all hits or are going to be hits, but we have 30 songs like that lying around, and that was one we just picked out of a bunch. And it was recorded on eight-track! That's a really low-quality format to have a Top 40 single on."

That's part of the charm, of course, along with the song's catchy, instantly imprinted chorus and a genial vibe built on a loop using the Andrea True Connection's 1976 disco hit, "More, More, More."

Details magazine described the single as "a pop lollipop with a chewy hip-hop center," and that's a fair description of Len, as well. The band's new album itself has a pleasing variety--a parody of Kraftwerk-style techno ("The Hard Disk Approach"), a pop soul ballad with gospel choir ("Crazy 'Cause I Believe"), a metal tune with a cameo from Poison guitarist CeCe DeVille ("Feelin' Alright")--but its heart is with old-school hip-hop. And not just old-school beats or attitude, but some of its original players, as well: Biz Markie brings his warbly off-key vocals and beat-box energies to "Beautiful Day" and "Man of the Year," while Kurtis Blow trades verses on "Cold Chillin'."

"The reason we go back to people like that and bring 'em into the crew is that there's no better chance to get to meet these people," Costanzo says. "And I've been thinking about these people for 10 years."

Talking to Costanzo, it's clear that he and his Len mates--D. Rock, Planet Pea (a k a Kudu5) and turntablists DJ Moves and the Drunkeness Monster--are hard-core hip-hop heads who look at old-school rap as a classic period in American music, much the way other generations look at the big band era or the early days of rock-and-roll and Motown.

"That's what we all grew up with in the late '80s and early '90s" in Toronto and Montreal, says Costanzo, who actually started out as a punk rocker--though with the same melodic inclinations that fuel Len.

"In my early teens, I got into the punk rock scene, and then, like everybody else, I got into Run D.M.C. and the Beastie Boys . . . the A-Team, Boogie Boys, Souls of Mischief, Del the Funky Homo Sapien. . . .

"I just love it because rap then was still innovative and creative," he explains. "That old-school feel has got so much more depth, it's so much more diverse. You can head so many different places with it, have so much more fun--you don't have to be so serious."

And, he adds, "people weren't worried about sampling because people weren't getting nailed for it yet. . . . It was a real good time." The band's love for old school is so deep that it used much of its major-label advance to round up vintage gear like Linn drum machines to use in the studio.

Len--named after a friend who happened to wander into a rehearsal just as the band was trying to decide on a name--came together in 1991 when then-20-year-old Costanzo moved from Montreal to Halifax and met up with DJ Moves and D. Rock. He plunged into a loose-knit community of hip-hop heads who gradually evolved into the Cryptic Souls Crew and the Len Crew. He also started his own hip-hop label, Four Ways to Rock, which put out the first two Len albums and may put out a follow-up album, not from Len but by the Len Crew, many of whom appear on "You Can't Stop the Bum Rush" (which plays off the title of Public Enemy's 1987 debut album).

"There's about 40 of us and we're all headed in the same direction," Costanzo says, explaining that "Len is us six, the people that represent the crew and go on the road, while the Len Crew is the 30 people behind us."

And soon, DJ Moves will start work on a disco album with Sharon Costanzo, who was first dragged onstage by her younger brother when he was still a punker.

"The only reason I do this is my brother's standing beside me," she says. "I don't do hip-hop, but I love it, especially the kind of rap they do, really up, party tracks. I mean, anything I can shake my [booty] to, I'm down with."