NEW YORK - It's 10 minutes to show time backstage at Late Night With Jimmy Fallon, and Ahmir "?uestlove" Thompson is wondering what the Roots have gotten themselves into.

"There are two sayings: 'The grass is always greener on the other side' and 'Be careful what you wish for,' " says the drummer and bandleader of the Philadelphia hip-hop-plus ensemble. Since March 2, when Fallon replaced Conan O'Brien at 12:35 a.m. on NBC, the group has been aptly introduced to America as "The Legendary Roots Crew."

The big man with the even-bigger Afro, which is now being puffed out to maximum mushroom-cloud size in a makeup room at 30 Rockefeller Center, pauses. And laughs.

"I cannot wait till we're off and can play a week on the road," he says, smiling. "Those shows will now seem like vacation time. This is way more work than imaginable."

Not that ?uestlove is complaining. In earning an unquestioned reputation as the greatest live band in hip-hop, the Roots - formed in the late '80s by Thompson and rapper Tariq "Black Thought" Trotter when they were at the Philadelphia High School for Creative and Performing Arts - kept a globe-spanning, 200-show-a-year, 2½-hour-a-night pace for more than 15 years.

"You know that secret room in [the video game] Mario Brothers, where there's a whole bunch of gold coins to collect? Like 200 gold coins?" he asks. "As far as getting gigs, that's pretty much been our life, from '93 until now."

After a month of shows, the Roots is finding its rhythm as a television house band. And Fallon, the absurdist boy-next-door Saturday Night Live alum, clearly can't believe his good fortune in snagging the group that he accurately calls - sorry, Max Weinberg 7 and Paul Shaffer's CBS Orchestra - "the best band in late night."

That rhythm starts with a daily two-hour Center City-to-Manhattan bus trip to a Midtown recording studio. There, the group writes original music for what the members call between-segment "sandwiches," and they work up witty snippets to play as guests are introduced. Serena Williams got E.U.'s "Da Butt," Glenn Close heard the Carpenters' "Close to You," and Anna Kournikova was met by Pat Benatar's "Hit Me With Your Best Shot."

The regimen has forced on the band an old-fashioned way to make music that is new to them: a bunch of guys sitting around the studio together bouncing song ideas off one another. Those results can be heard on-screen as well as on How I Got Over, the Roots album due out in July.

"The synergy of a bunch of world-class musicians in a room together, there's definitely something to be said for that," says James Poyser. Clad in a T-shirt with Barack Obama's head attached to Afropop pioneer Fela Kuti's body, the keyboardist-songwriter-producer and sometime Root - "I've called myself 'a stem' for years" - has joined full time for the show.

The broadcast platform is giving the group "a new life, so to speak," Trotter, his Yankees cap cocked to the side, says at the Midtown studio. In addition to him, Thompson, and Poyser, the lineup includes guitarist "Captain" Kirk Douglas, percussionist Frank Knuckles, bassist Owen Biddle, sousaphonist Damon "Tuba Gooding Jr." Bryson, and keyboard player Kamal Gray.

"It's exposing the Roots to a late-night-TV demographic who aren't necessarily familiar with what we do. It's shameless self-promotion, every day," says Trotter, who's also an actor featured in the indie flick Explicit Ills and has other films in the works.

The Roots, it seems, has been playing live every day since Thompson and Trotter and original bassist Christian McBride used to busk for tips two decades ago on the corner of Fifth and South Streets on Saturday afternoons.

Some members are now settled in the Philadelphia suburbs with wives and children. So, Trotter says, moving on up to a steady gig at 30 Rock "just felt like the right move."

"It's the one good thing everybody says about the show," Fallon says by phone the morning after the April 1 show. The previous night, the Roots had warmed up the crowd off-camera with a tribute to Fela Kuti, then pulled a revamped cover of the Memphis soul song "I'm Afraid the Masquerade Is Over" out of its musical trickbag for a curtain-to-the-couch walk by ER actor Noah Wyle. Revising David Porter's lyrics, Black Thought sang: "It's over! Your medical career is over. . . ."

"People will say, 'The show has this problem, and this is good, but that's bad,' " Fallon says. "But the constant is, 'Man, the Roots are fantastic! They are just phenomenal!' And they really are. The warm-up alone - they make this entrance that's unlike anything you'll ever see. Damon [Bryson, the sousaphonist] comes across the stage, and people don't know what's going on. It's mind-blowing."

The Roots may be settling in as a late-night house band, but the members have hardly given up life on the road. Except for Douglas and Biddle, who live in New York, all typically commute to work on their tour bus.

Then there's the weekly session at Manhattan's Highline Ballroom that is billed as The Roots Present The Jam.

After the Fallon taping was over that April evening, they took the stage at the Highline at 11:45 for a deliciously adventurous show that included improvisation with Living Colour guitarist Vernon Reid, African-German singer Ayo, members of the Brooklyn global-beat collective Antibalas, flamboyant "dirty gospel" showstopper the Rev. Vince Anderson, and two groups - the Subway Band and the Stumblebum Brass Band - that the Roots found playing for tips by the New York subway.

"This is where the Roots came from," says Trotter, as he comes on stage in the meatpacking-district club. "This is an example of it all coming full circle."

Talking about playing on the Fallon show, Poyser says focusing the band's wide-ranging musicality on TV snippets is more satisfying than it looks. "We're playing through the break, so we do get to play," he says. "I feel sorry for the audience at home, who doesn't get to hear what we're doing, because we're killing."

Douglas, though, says the Highline jams are the band's opportunity to stretch out. "That's us being let loose," he says, "let out of our cage."

Besides the Highline gigs, Richard Nichols, the group's manager, figures the group will do an additional 60 to 70 shows this year on weekends and during the members' 10 weeks off.

This month, they'll open for Dave Matthews at Madison Square Garden, and this summer they'll go out on weekends with the Rock the Bells hip-hop tour. On June 6, they'll host the second annual Roots Picnic at Philadelphia's Festival Pier, with TV on the Radio, Santigold, Asher Roth, and Public Enemy.

It came as a shock to many fans when it was announced that the band - whose recent albums Rising Down (2008) and Game Theory (2006) were particularly hard-hitting and politically agitated - was taking a job as a late-night house band. Were the Roots getting soft?

To the band, it made perfect sense.

"It's a change of pace that shows off a different side of the band," Nichols says. "People are complex. And these are uncertain financial times. Our workload was stable, and the money was cool. But you just never know."

On camera, Trotter's role isn't as large as it is on stage, though he does sing in a recurring bit called "Slow Jam the News." And the band is in comic segments such as the faux reality show 7th Floor West, a takeoff on MTV's The Hills. "It's a chance to show some of the other facets of my personality," says Trotter, who has a solo album coming. "There's a comedic side, a less-serious side, a less-militant side."

How I Got Over, the new Roots album, will display an Age of Obama optimism. "There's still a sense of drowning desperation, but now there's a glimmer of hope," says ?uestlove.

The title comes from Clara Ward's gospel hymn, though Nichols says the album's vision is "like a cross between Mahalia Jackson and Melvin Van Peebles. That title could be about Obama. Or it could be about the Roots on Jimmy Fallon." Musically, says ?uestlove, the album recalls earlier, less-dense albums like 1993's Organix.

Fallon first approached the Roots last April after a show in Los Angeles, at the urging of his friend Neil Brennan. Brennan is a former producer on Comedy Central's Chappelle's Show, where ?uestlove was the de facto music director for a season and a half.

"I was just blown away at how diverse they are," Fallon says. "They went from a Roots song to a Soulja Boy song to a Guns N' Roses song, and then did, like, 'In-A-Gadda-Da-Vida.' And then back to another Roots song. I was like, what?! . . . Then I went back to meet them, because, you know, talent is one thing, but I have to live with these guys. You see them more than your own family. And they couldn't be nicer."

The Roots' workload, and commute, can be grueling. "We go to bed at 4:49 and get up at 5," ?uestlove jokes. Still, "just to be able to come up here and be able to go back to our families every night - that's great," says Knuckles, who lives in Lansdowne with his wife and three children.

With their schedule, isn't it inevitable that the Roots will have to move? Is Philadelphia about to lose one of its most treasured musical resources?

Trotter, who commutes daily from Lansdale to Center City before boarding the bus to Manhattan, plans to move next year. And ?uestlove is exploring the expensive possibility of obtaining a second home, in Manhattan.

"But I put a lot of work into my [Philadelphia] studio. And I really, really like my house in Northern Liberties. I love Philly too much," he says. "I'm willing to put up with sleep deprivation."