When rock 'n' roll was the dominant force in music during the late '60s and early '70s, Three Dog Night was one of the power groups. They completely filled some of the biggest arenas in the country, they commanded up to $40,000 a performance and they interpreted some of the most memorable songs of the era.

Monday night, they were back. And though they played to a slightly smaller audience at Lagoon, and I assume they did it for less money, they still interpreted some of the most memorable songs of the '70s - and they did it as well as ever, even without founding member Chuck Negron.Frankly, I'd forgotten, over the years since they broke up, how good their harmonies are. But the rich tones familiar to fans have gained a maturity and a depth over the past 15 years that I hadn't quite expected. If anything, I thought they might be a little rusty or lack some of their youthful edge. I was wrong.

Co-founders (minus Negron) Cory Wells and Danny Hutton bring the same style and sound to the music they made famous (or did it make them famous?). Paul Kingery fills out the vocals by slipping into Ne-gron's old shoes, and they seem to fit him well. I don't think anyone noticed that a new voice was singing "Joy to the World." It certainly didn't slow those who were clapping and swaying and singing along down at all.

Three Dog Night rose to the top of the music world in a very short time, without much fuss. In 1975, they faded out quietly, when the incredible amount of time they were spending on the road lost its appeal.

Two years ago, they started talking to each other. While tracking down a rumor that a group was trying to capitalize on the Three Dog Night name, Wells and Hutton discovered that they'd both been approached by the same people to stage a reunion. And they were both a little interested. So they got together a group that also includes original keyboardist Jimmy Greenspoon, Scott Manzo on bass and Mike Keeley on drums, and they rehearsed a little.

And, because they sounded good - better, in fact than before, because of their maturity, according to Wells - they decided to take their act on the road.

The 13-song early show Monday began slowly and it took the crowd a few minutes to get warmed up. But the pacing of the music (very seldom interrupted for chitchat) soon caught up with the audience and by the end of the show, no one was sitting down.

The sound was clearer and more controlled than I've ever heard at this particular venue. "Family of Man" was hard to understand, but by the time Three Dog Night moved on to "Black and White," the problems had been corrected and the group had an album-calibre sound.

With a big difference: you don't usually listen to an album under a beautiful blue sky, cradled in the curve of the mountains.

The songs varied from the jazzy "Sure as You're Sitting Here" to the pure rock "Liar" (by far the most unbridled and noisy offering). The most popular numbers, though, were the Three Dog Night standards - the ones guaranteed to take listeners back to a certain time and place and group of friends from the past. Songs like "One," "Shambala," "I've Never Been to Spain," "Mama Told Me Not to Come" and "Old Fashioned Love Song."

Once the pace picked up, it kept building until it got white-hot.

Then they brought out the one song everyone knew they'd sing before they called it a night: "Joy to the World." And as the saga of Jeremiah the Bullfrog unfolded, people ranging in age from infant to 50 started clapping and stomping and singing along. That may be the only song, besides "God Bless America" that every U.S. citizen knows by heart.

The obligatory Utah concert encore was, for once, very much deserved and very heartily given. The enthusiastic audience was rewarded with a jumpy, boisterous rendition of "Celebrate."

The baby boom has a created a time warp. As I joined the throng leaving the concert, I heard a middle-aged father turn to his teenage son. "Now that, young man, is music. Not like the stuff you call music." The same thing my dad said about Big Band sound.

And you know something? They're both right.