CROSBY, STILLS, NASH SING NOSTALGIA

Graham Nash introduced “Carry On,” the first encore at Crosby, Stills & Nash’s Tuesday show at the Pacific Amphitheatre, by saying, “Here’s a song we’ve been singing a long time.” He made it sound as if it was a rare dip into the past, but that 15-year-old chestnut was hardly the only number that old.

In fact, the trio trotted out an array of moldy-but-goody pieces, underscoring its recent de-evolution into a nostalgia act masquerading as a fully active pop force. The often ecstatic crowd response during the nearly two-hour show demonstrated just how effective CS&N; has become at generating secondhand emotions: The feelings their shows now elicit are ones you remember , rather than new ones you experience directly.

Despite these shortcomings, the show still carried a few poignant moments. One came when Nash announced that the group’s food-drive campaign yielded 700 pounds of donations. However, the most moving were produced by the legally and pharmaceutically troubled David Crosby. At the outset, he looked somber and disconnected. But, perhaps sensing that the audience was really pulling for him, he began to put more of himself into each number, finally singing his heart out on “Long Time Gone.” The crowd roared, and Crosby looked jubilant, beaming and exchanging a high-five slap with Stills. From then on, like someone out of “Cocoon,” Crosby appeared rejuvenated and vigorous.

Opening this blast-from-the-past revue was the Band, which continues to cover for Robbie Robertson’s absence with four musicians. This made for a big, propulsive attack (anchored by two drummers and two bassists), but never approached the magic associated with the Band in its heyday. Does the group really want to erode its reputation by functioning as an arena-rock bar band?

The same bill closes a two-night stand at the Greek Theatre tonight.