Last night, the Rolling Stones opened the first of three sold-out Capital Centre concerts with the compelling chords and visceral philosophy of "Under My Thumb." Then they spent much of the next two hours struggling to maintain a grip on themselves, the sound system and the weight of their history.

After a desultory opening set by veteran R&B singer Bobby Womack, there was a long period of anticipation. It eventually resolved for the 19,000 fans by the dimming of lights, a deafening roar of exhilaration and release, and the beauty parade entrance of the Stones: rock steady drummer Charlie Watts, serene bassist Bill Wyman, naughty guitarist Ron Wood, and those perpetual bad boys, Glimmer Twins and rock legends, Mick Jagger and Keith Richards.

The stage on which the Stones methodically appeared with their cordless instruments was a wonder of proper sightlines and provocative lights. If they sought to establish momentum with "Under My Thumb," they succeeded more in realizing the audiences' expectations. Despite Jagger's flip poses and remarkable energy, one sensed in the slouches and dangling cigarettes of the two guitarists a bit of "It's Only Rock 'n' Roll, So You'll Like It." With tickets starting at $17.50, no one was looking forward to being disappointed.

The Stones are the archetypal rock band, and the frequent ecstatic moments in last night's show confirmed that few others can match them for authority, intuition and execution. But the equally frequent shortcomings betrayed the group's age and possible callousness.

There is a disquieting feeling that this tour is neither an attempt to turn back the clock (the Stones seem quite comfortable showcasing their roots without resorting to insipid nostalgia) nor an attempt to say goodbye with style. One senses instead the ugly hand of commerce prodding the Stones to send the collection plate around one last time before bolting from the church.

First of all, it must be said that the fans loved it without reservation. The Stones, touring infrequently, have drawn absolution more frequently than any band in history. One excuses their sloppiness, particularly when the playing is spirited. At the same time, there's that old question: Is it real or is it memory, not only for the band, but for the audience? No one knows the answer.

When it was good, it was very very good. Mick Jagger is still the consummate cheerleader and rock 'n' roll singer, still possessed of the most endearing and enduring backside in rock. He may be a virtual catalog of stage posturing but there's an underlying (and perhaps slightly manic) good humor to his act. Jagger seemed most comfortable with the slow and mid-tempo tunes, particularly "Just My Imagination," "Time Is on My Side" and "Tumbling Dice." The venom was still evident on classics like "Honky Tonk Women" and "Brown Sugar" -- Jagger as the Glim Rambler prancing around the stage, strutting like a cool cat in heat.

And there was Richards, looking unfortunately like the Glim Reaper, a frightening, ashen apparition whose haunting face reflects the down side of rock 'n' roll. When Richards is on, as he was only occasionally last night, he can push Watts and Wyman into one of the most tight-fisted rhythm sections in rock.

Even with Wood alternating on lead and rhythm, Richards is the one who must push the music forward if the Stones are to roll. Last night, he looked like he needed a jump start. He almost got it from tenor saxophonist Ernie Watts, whose blistering solos were the highlight of too many songs. Ian Stewart and Ian McLagan provided adequate but not exhilarating keyboard support.

It didn't help that the overall sound at the Capital Centre was so muddy that guitar solos were seldom distinct, leaving Jagger's voice and Watts' sax to cut through the night air. When the basic sound was lean and hard -- a rock-solid "Miss You," an insistent "Let's Spend the Night Together," a racing "Shattered," a back-to-the-blues-basic "Black Limousine" and a challenging and vitriolic "Beast of Burden" -- the Stones were exciting and managed to live up to their reputation.

When the going got rough -- a dreary segue from Eddie Cochran's "20 Flight Rock" to "Going to a Go-Go," or Richards' bleating on "Little T&A" -- well, the going got rough. On "Let Me Go," Jagger ran into the audience with the kind of protection that would net Herve Villechaize a touchdown in the NFL. If that's taking chances it's hardly worth the risk.

Other gimmicks included a cherry picker that brought Mick Jagger to the stage for "Jumpin' Jack Flash," thousands of balloons dropped on a suspecting audience and the ironic choice of "Satisfaction" as a closing number.

The Stones skipped most of their mid-'70s work, but gave generous samplings of "Some Girls," "Emotional Rescue," and their most recent album, "Tattoo You." One kept waiting for the cutting edge, in Jagger's insistent vocals, in Richards' and Wood's crude guitar, something to reaffirm the primal urge of rock 'n' roll that the Stones are supposed to provide.

One got, instead, predictable dynamics and too few hints of the passionate audacity and perennial delinquency that marks the best Stones work. Jagger still worked the crowd like a preacher, but he was delivering a sermon that's become too familiar. Tonight, they'll probably sound like the Rolling Stones that people were expecting last night. It's a mysterious well they keep going back to. Sometimes it runs dry, and sometimes it doesn't.