A folk/bluegrass super . . . lineup

“It really makes my skin crawl. I’m in a band with a guy who was in a supergroup,’’ says Heartbreakers’ keyboardist Benmont Tench, referring to the Traveling Wilburys, the ’80s outfit his boss, Tom Petty, moonlighted in with guys named Orbison, Harrison, Lynne, and Dylan. “We’re a bunch of people who are in other bands.’’

Despite Tench’s objections, fans of pop, roots, folk, bluegrass, and country music who pay attention to liner notes will undoubtedly think the WPA membership list is pretty damn super. The octet, which formed following various cross-pollinations over the years at the Los Angeles club Largo, comprises musicians who have played on hundreds of albums.

Some, like main singer-songwriters Glen Phillips and Sean Watkins, are identified with specific groups - ’90s alt-popsters Toad the Wet Sprocket and vaunted bluegrass trio Nickel Creek, respectively. Others are revered journeymen. In addition to his work with Petty in the Heartbreakers and Mudcrutch, Tench has played on records by Johnny Cash, Neil Diamond, Sheryl Crow, the Dixie Chicks, and scores more. Ditto for WPA steel guitar/dobro player Greg Leisz, who, as one of the most in-demand session players of the past 20 years, has picked for everyone from Dwight Yoakam to the Smashing Pumpkins. The rhythm section of bassist Davey Faragher and drummer Pete Thomas has also gotten around but of late come directly from Elvis Costello’s backing group, the Imposters. Luke Bulla, the third member of the core trio, has played his fiddle with a laundry list of country and bluegrass greats including Ricky Skaggs and Lyle Lovett. Watkins’s sister and Nickel Creek bandmate Sara also pitches in on the group’s sterling debut, “Works Progress Administration,’’ released in September.

“We went into - I don’t even think it was optimistically - we just wanted to make music together, and that’s as far as we thought. If we’d been thinking a little bit more clearly we might not have done it,’’ Phillips, says of the unwieldy, overscheduled group. “In terms of the business, it doesn’t work at all. But it works in all the ways that I’ve wanted making music with people to work.’’

The album, which takes its name from FDR’s arts-based economic stimulus concept (as does the group), indeed works. Phillips’s genial pop melancholia meshes nicely with Watkins’s equally melodic and pensive folk musings. Shaded harmonies, tasteful solos, and intricate arrangements are the order of the day as lives and loves are incisively examined.

“It’s a good cross-sectional representation of all of them in the band,’’ says Largo proprietor Mark Flanagan, a longtime friend to almost all of the members, particularly Phillips. “I was happy to see this as an outlet for him to collaborate with other people. And Luke and Sean being equal to him is really strong for him because it pushes him a bit too.’’

“I can get pretty depressed about my post-Toad experience,’’ Phillips says of his smaller-scale solo career of the past decade. “But it’s been amazing to me this project and to realize it was a labor of love for everybody involved. The fact that these people would be willing to play with me if we were paying their book rate would be awesome. The fact that they did not have to give their time the way they did or go out on the road, it’s awesome.’’

Given their other commitments, not all of the WPA-ers appear at every date. The primary touring version, which plays two shows at Club Passim tonight, features Phillips, Watkins, and Bulla backed by drummer Jerry Roe and Soul Coughing bassist Sebastian Steinberg.

But regardless of who’s playing where, all of the members of WPA get a charge from collaborating in a way that makes them hopeful for future projects.

“They’re just really great people to spend time with who happen to be fantastic musicians,’’ says Tench, who says he continues to learn from his younger compatriots. “It’s been a very, very long time - 20 years or something - since I’ve had that experience of just being in the van together loving each other’s company, playing each other’s music, looking forward to the show every night. To have the camaraderie combined with the quality is awesome.’’

Sarah Rodman can be reached at srodman@globe.com.