by Sarah Rodman

Mick Fleetwood was browsing in a Philadelphia Tower Records store last week when he was pleased to find Fleetwood Mac's new album, "Say You Will,'' prominently displayed among the store's top sellers. It now sits in the top 15 of the Billboard albums chart and is quickly on its way to gold status after a month in release.

Also, the band's tour is playing to packed houses and glowing notices across the country. The current incarnation of Fleetwood Mac - Fleetwood, bassist John McVie, singer Stevie Nicks and singer-guitarist Lindsey Buckingham - comes to the Worcester Centrum Centre tonight and tomorrow.

"It's certainly really gratifying,'' says the towering drummer on the phone from the City of Brotherly Love. "There we are (on the racks) with a whole myriad of people that quite frankly I haven't heard of who are vastly successful, rappers and God knows what else, and there's Fleetwood Mac. So it's doing extraordinarily well.''

Although the 55-year-old Brit has some experience with doing extraordinarily well - the band's 1977 album "Rumours'' is the fifth best-selling album of all time, with more than 18 million copies sold in the United States alone - his expectations were not high for an album of all-new material after the band had spent several years out of the spotlight.

"You always live in hope that things are going to go well but this is a very different climate. The reality is, we're not 18 years old anymore and the people who go out and buy records are certainly a very different demographic, and radio is hard to get and we don't get MTV, so with what's happening it is fairly extraordinary.''

What might be even more amazing is that "Say You Will'' is a solid and respectable return to peak form for a band that has taken many turns, and made many personnel shifts, in its 36-year history.

The album began as a Buckingham solo record until Warner Brothers showed more interest in a Fleetwood Mac release. Buckingham, who plays guitar like a monster throughout, contributed nine songs. The best of these, including "Miranda'' and "What's the World Coming To,'' combine acoustic and electric textures and great pop hooks. Nicks comes through with the other nine songs, including several ethereal keepers sung in her deepening, yet still compelling, rasp. The lilting "Peacekeeper'' already has become a radio hit.

The (overlong) album is by no means a retread of "Rumours'' or "Tusk,'' but the more organic, laid-back tone of "Say You Will'' does evoke the late-'70s work more than the likable but synth-heavy pop radio singles from the late '80s and early '90s releases.

"It's the best of the `Tusk' sensibilities meeting where we were with `Rumours' in terms of an awareness that this is the style of the band and the style of the writing. I think that's where we ended up with this album, which is not a bad place to be,'' says Fleetwood, who is the only member other than McVie to be with the band from the beginning.

The latest lineup change comes with the departure of singer-keyboardist-songwriter Christine McVie, John's ex. She had been with the band since 1970 and contributed such hits as "You Make Loving Fun'' and "Don't Stop.'' Her willowy alto and sweet pop sensibilities are missed on the new album, but Fleetwood says it was surprisingly easy to soldier on without her.

"It really wasn't too traumatic, to tell you the truth,'' Fleetwood says of Christine McVie's departure after the 1997 "The Dance'' tour. He compares the band to "a good regiment. We just closed ranks and this is what we came up with. Her legacy is so affirmed in our history, and it's an important one that will never go away.''

Fleetwood misses McVie on the road, but understands her wariness of the show-biz machine. "She made it very clear that it was not for her anymore, doing what we do - running around, having to be available all the time, she didn't enjoy flying - she'd just had enough.''

The other members have yet to reach their limits, however. And with the soap-opera story lines of fractured intraband romances, copious drug abuse and ego-driven transgressions behind them, Fleetwood thinks there might be a future for the foursome beyond this tour.

"We're basically committed to doing all of that stuff as long as we're all happy doing it,'' says Fleetwood of potential recordings and tours. "I would love to think that we're going to make more music, and I think all of us are open to that. It's going to be a very long tour and at the end of it, if we're all still smiling, we'll say, `Why the hell not?' ''

One thing working in their favor is that fights among band members - and they are still numerous, says Fleetwood - are conducted in a healthier fashion.

"It is different because we get a resolve out of it, nothing gets shoved under the carpet,'' says Fleetwood of creative differences over everything from the set list to album sequencing. "In the old days, we were all on such a roll and doing our own thing, and things weren't really spoken about.

"And to be blunt, we're not doing things that are mind-altering in any way anymore,'' he says with a laugh, "so it has greatly changed.''

Luckily, the quality of the songs remains the same.