You might expect someone in a band that was reunited after a decade and is now in the midst of its first American tour in 14 years to offer some deep, underlying reason for the group's renascence. But try as he might, Pentangle's Bert Jansch can't come up with one.

"Some bloke just asked us if we could get together again for a show, and we did," quips Jansch, a genial Scot not given to long-winded replies. It was Jansch's gift as a songwriter, coupled with his sterling guitar work and appetite for the eclectic -- an appetite shared by his colleagues in the band -- that helped make Pentangle such a popular and pivotal folk-rock ensemble in the mid-'60s, paving the way for similarly minded bands like Fairport Convention and Steeleye Span.

This isn't the first time the members of Pentangle tried to get back together; only the most successful. "I guess it's the new blood that makes it work this time," Jansch says, referring to guitarist and fiddler Mike Piggott (who replaced John Renbourn) and bassist Nigel Smith (who more recently took Danny Thompson's place).

Whatever the reasons for its rebirth, it appears this edition of Pentangle will be around for a while. The British quintet, which appears Thursday at the Birchmere, released "Open the Door," a widely acclaimed album, last year, and Jansch suggests the best is yet to come.

"The new album "In the Round" is a lot better," he insists. "It has the current lineup, and we all contribute material -- which has always been a strong point with Pentangle."

Because the new songs take advantage of the band's recent change in instrumentation -- specifically, the coupling of Piggott's electric guitar and fiddle with Smith's electric bass -- Jansch also feels Pentangle's music has "a lot of new colors now." In fact, he says, "It's a completely different feel on this album. Believe it or not, I thought the last one was a bit staid, a bit contrived."

If the new record is anything like the band's previous releases, it will not only reflect Jansch's lifelong love of country blues and finger-style guitar, but the varied tastes of his bandmates as well. Blues, jazz, folk, rock, Celtic, classical, Indian music -- it's all fair game, according to Jansch, and Pentangle's discography bears him out. At one time or another the band has incorporated all of these influences in its music, sometimes with strikingly original results, sometimes less successfully, but nearly always with an instrumental precision worthy of a chamber ensemble.

From the outset, says Jansch, even when Pentangle was just beginning to make a name for itself on London's West End 20 years ago, the music evolved naturally, without any one band member leading the way. Playing one kind of music for very long never appealed to anyone in the band, so Pentangle, almost unwittingly, began to capitalize on its individual strengths and interests.

"I remember I was very much into jazz bassist and composer Charlie Mingus, among other people, at the time," Jansch recalls. "And if someone was listening to Indian music -- for instance, I've listened to a lot of Ravi Shankar -- the Indian flavor would just show up in our music sooner or later. It was all very natural."

Apart from his songwriting, Jansch feels his real strength lies in his ability to "fuse musics you wouldn't ordinarily find together." He points to vocalist Jacqui McShee's grounding in English traditional music and drummer Terry Cox's extensive background in jazz as other reasons for the band's appeal. As for newcomers Piggott and Smith, Jansch has spent much of the past five years working with them in both duo and trio settings, so he feels right at home performing with them.

Despite the diversity of his recordings, the music that first prompted Jansch to pick up the guitar comes as a bit of a surprise. Born in Glasgow and raised in Edinburgh, he was smitten by the jug-band-like British skiffle craze in the early '50s. By the time he was 16, he was already hitchhiking all over Europe, playing wherever he could and, more importantly, discovering the music of American blues artists.

"All of a sudden you could find these records in Europe by people like Big Bill Broonzy, Leadbelly and Brownie McGhee in stores here and there," he recalls, ticking off the names of some of his early idols. Years later, Jansch would team up on record with another blues aficionado, guitarist John Renbourn, before the two helped put Pentangle on the map. Although the group was an immediate success, Jansch says it wasn't until Pentangle was nearly on the verge of breaking up in the mid-'70s that he finally realized the impact the group had had on the growth of acoustic music on both sides of the Atlantic.

And the audience is still there, Jansch reports from midtour, though he admits that American audiences "tend to be more studious, don't you think?" than their British counterparts. Then, pausing a moment, he adds, "Of course, in Britain most of the music you hear is in pubs, so people are much more apt to get drunk and fall about.