ANYONE OF baby-boomer age has memories of slow-dancing to "Nights in White Satin" in high school -- it's right up there with "Stairway to Heaven" for All-Time Prom Theme Champ.

"Yeah, 'Nights' is always the last dance. And people get married to it, I'm told," says Moody Blues guitarist Justin Hayward, who wrote the stately "Nights" and many other melancholy Moody melodies, custom-made for daydreaming to in our adolescent rooms.

Hayward, 44, is not very Moody at all. On the contrary, he's friendly and forthcoming on the phone from Atlanta, where the band is preparing to play an outdoor show. He says he's noticing a new, younger audience these days, apparently attracted by the band's recent hit "Your Wildest Dreams." But longtime fans still show up, loyal to a band that's stayed remarkably intact since 1966. Four of five original members remain -- Hayward, bass player John Lodge, drummer Graeme Edge, and flutist Ray Thomas. Ex-Yes-man Patrick Moraz replaced keyboardist Mike Pinder in 1981.

"Nights in White Satin" nearly didn't happen, Hayward says. The very young Moodies were supposed to be using their three weeks of studio time to record a rock group-meets-symphony orchestra version of Dvorak's "New World Symphony" to show off Decca's new Deramic Sound System album line. Instead, the Moodies made "Days of Future Passed," a suite of original songs.

They were tapped for the project by the label because they were among the first pop groups using the Mellotron, a sort of primitive sampler, which played tapes of orchestral instruments through a keyboard. The Mellotron became their signature.

"It gave us that orchestral sound -- it set our direction for 'Days of Future Passed,' but it was such a temperamental instrument, a nightmare to play," Hayward says. "When you pressed a key down, you only got eight seconds of taped sound. It wasn't even a tape loop, it was just one piece of tape for every key. The tape would go over a tape head, and then at the end it would go sproing, and go back to the beginning. So you could be getting really carried away and emotional about some sort of musical phrase, and the whole thing suddenly would go boing boing boing! I remember one night Mike came out and played one chord and all the tapes came spewing out the back, all over the stage."

The Moodies showed Bugs Bunny cartoons while Pinder repaired his instrument.

Now the Moodies uses trendy electronic samplers to create that Mellotron sound, of course. But Hayward hangs on to the guitar and amp he's played since the '60s.

The Moodies made "Days of Future Passed" at a time when everyone was doing "concept albums" -- the Beach Boys had done "Pet Sounds," the Beatles came out with "Sgt. Pepper," and the race was on to see who could concoct the most imaginative and outlandish projects. Hayward says "Days" was inspired by an obscure album called "The Zodiac" by an American group called Cosmic Sounds.

After a bit of record-company resistance, "Days of Future Passed" was released and camped out on the charts for two years. Fifteen more albums (including a live recording and two greatest hits packages), with ever-trippier titles, followed: "In Search of the Lost Chord," "On the Threshhold of a Dream" "To Our Children's Children's Children" . . . up to 1988's "Sur la Mer." And from them came a chain of unlikely hits, none of which would be pegged as surefire singles today. Hayward says his band always did just as it pleased. Still does.

"Obviously, we haven't been influenced by fashions or trends," Hayward says. "And because of that we've seen a lot of other things come and go -- and we're still here."

Hayward says he routinely gets advice and pressure from record-company types, who mean to bring the Moodies commercially up to date. As if anyone wanted that to happen.

"It's all these little subtle things, like sending you particular kinds of heavy-metal records and saying 'This is the drum sound that you've gotta have now.' Or, 'You've gotta have a song that gets to the hook within 20 seconds or they're not going to put it on a tip sheet.' I can't honestly say I've ever gone into the studio and been influenced by that stuff."

And the Moodies don't put on a gimmicky, video-oriented show, either.

"We really rely on the music and the songs," Hayward says. "And there's such a wealth of songs to draw on, simply because of the time span. The other day we were trying to work out a set list and it was like, what do you leave out? We're trying to do things from most of the albums. But there are a lot of things -- 'Nights,' 'Ride My Seesaw,' 'Question' -- that we couldn't get offstage without playing."