LONG before the Moody Blues became a touring phenomenon and a PBS staple in America -- a classic rock band with strings attached -- the group explored the possibility of performing in symphonic settings throughout the United Kingdom. That's when all four members of the band reached the same conclusion: traveling light was out of the question.

"You can't do it from an English standpoint because there's only a few professional quality orchestras over there, so you'd have to travel with one," says the Moodies singer-songwriter and guitarist Justin Hayward, calling from a tour stop in Kansas City. "What we quickly found out in America is that it's unique in the world. Almost every town has a professional quality orchestra. Actually, a lot of people who come to our concerts don't even know they have an orchestra in their town until they see us."

Appearing with the Prince William Symphony Orchestra at Nissan Pavilion Wednesday night, the British quartet discovered early on that rehearsing with regional ensembles is more hindrance than help. Hayward explains: "In the beginning, when we realized that it was possible to do this every night with a different orchestra, we thought we should rehearse with each one, but we found that the orchestras were distracted by us -- the noise we make and our general fuss and chatter. The orchestra director decided it was better to rehearse without us. If everyone plays what's written, it will all work out."

And as Hayward hastens to add, the band's symphonic collaborations have not only worked out since they were initiated seven years ago, they've surpassed all expectations, revitalizing the group's spirits and broadening its audience. It all began with "A Night at Red Rocks," a 1992 concert featuring the 88-piece Colorado Symphony Orchestra and celebrating the 25th anniversary of the release of the group's landmark album, "Days of Future Passed." The impact of the concert, and its frequent airings on PBS, was startling, Hayward says.

"The idea of a rock band, particularly a classic rock band, playing with an orchestra really appealed to a lot of people -- more than we could have hoped for. But the idea seems to have only worked with the Moodies. I've seen other people do it, but it doesn't come off for me -- it's just a backdrop with strings. We have identifiable pieces of music that the orchestra plays -- in a sense, they have their own hits to play from `Days of Future Passed' -- the overture and other pieces."

The success of the concert and the PBS broadcasts was immediately felt at the box office, as the band's audience swelled.

"I think a lot of older people who saw the PBS airings realized that our concerts were safe -- they weren't going to have a rough time at one of our shows," Hayward says. "At the same time, we suddenly saw all these young people coming to our concerts. They seem to like a lot of the music we made on our first few albums. Maybe that's because those records deal with the innocent expression of youth. I hope that's the case."

The trick now, he says, is to integrate songs from the band's new 14-track album, "Strange Times," into its shows without alienating fans who've come to hear the hits.

"I know how that feels when you've gone to see someone perform and instead of performing what you want to hear, they play a lot of new stuff and you go, `aargh.' So we are mindful of that. But so far the reaction to the new songs, particularly the new single `English Sunset,' has been great. People really seem to respond to it."

Of course, Hayward and his bandmates -- bassist John Lodge, flutist Ray Thomas and drummer Graeme Edge -- are old hands at this sort of balancing act. Hayward and Lodge joined the band in 1966 and played a key role in reshaping its music after the departure of singer and guitarist Denny Laine, who later surfaced in Wings.

Laine put the band on the charts with the hit single "Go Now," an R&B tune that could have been recorded by the Rolling Stones. Hayward admits, however, that he and Lodge didn't share Laine's passion for rhythm and blues.

"I came to the band after Denny had left and it seemed to me that the band had never really jelled. Denny had a great R&B voice and when he left he took that with him. So we were forced to change. I mean, I had gone back to live at home. Our price had dropped to around 20 pounds a night -- the price for a semi-pro band, so the only way was up. Literally, the moment we threw away our blue suits and stopped playing rhythm and blues and started playing our own stuff, everything changed for us. It happened that fast."

THE MOODY BLUES -- Appearing Wednesday at Nissan Pavilion. * To hear a free Sound Bite from "Strange Times," call Post-Haste at 202/334-9000 and press 8109. (Prince William residents, call 690-4110.)